What is National Health Insurance?
National Health Insurance (kokumin kenko hoken) is a public health insurance system for the self-employed, farmers, the retired and those who are not covered by another insurance system.
Those who do not join an insurance managed at a place of employment or those not receiving social welfare must join this system.
Those who do not join an insurance system may have to pay the full amount of medical costs incurred.
Those who withdraw from the insurance offered at their place of employment should apply to join the National Health Insurance.

(If you join the National Health Insurance system)
(1) You will pay 30% of costs when seeing a doctor.
(The cost of items not covered by insurance must be borne by the individual.)
(2) When a child is born to an insured person, that person may receive a lump sum payment after birth for child rearing expenses.
(3) At death, payments for funeral expenses may be received. Other payments and benefits are also available. Enquire at your city, ward, town or village office.

(How to join the system)
Those foreign nationals who have registered as aliens and have stayed in Japan in accordance with the immigration law for more than 1 year may enter the system. Those who have stayed in Japan for less than 1 year but out of consideration for their purpose for entering the country are considered as having stayed over 1 year can also join the system.
(1) Applications should be made at the city, ward, town or village office where one’s alien registration was made.
(2) Required items
l Certificate of Alien Registration or toroku genpyo kisai jiko shomei sho
l Seal (if none, a signature will do)
l Document to prove you have stayed in Japan over 1 year
(Passport, school/college identification card, study project, etc.)

(National Health Insurance Card)
One National Health Insurance Card is issued per family.
When seeking medical treatment, bring the insurance card to the hospital or clinic and show it at the reception desk.
If members of the family live separately, an extra copy of the National Health Insurance Card can be issued.

About insurance premiums
The annual insurance payment is calculated on the insured individual’s annual income (municipal tax valuation) and the number of people in the family as one unit.
People over 40 years old and under 65 years old must also pay an additional premium for Nursing Care Insurance (kaigo hoken).
Since there is no income prior to your first year in Japan, you will be charged the minimum rate during the first year. From the second year, you will be charged according to your income.

Annual insurance payments are decided according to your municipal tax and are paid in 10 installments from June to March the following year. An insurance payment bill will be sent from the city, ward, town or village office. Payment should be made by the due date at a bank or post office. If the appropriate application is made, payments can be made automatically by your bank and transferred from your bank account.

Since joining a public health insurance system is compulsory, you must join either the health insurance system at your place of employment or the National Health Insurance system.

As public health insurance is compulsory, you are required to subscribe to either National Health Insurance or another public health insurance offered by your employers. Although you are allowed to apply for the National Health Insurance at any time, you will also be asked to pay either for the period starting from the day you completed alien registration to the day you became insured, or for a period specified by the relevant law.

In cases of disaster, unemployment, bankruptcy, etc. when it becomes difficult to pay insurance premiums, it may be possible to receive a remission from payment.
If insurance premiums are not paid, the total cost of medical expenses may have to be borne and benefits may be suspended.

The following must be reported
The following should be reported within 14 days:
(1) A change of address (When you have moved within the city, ward, town or village)
(2) Moving in or out a city, ward, town or village
(i) When moving out of the city, ward, town or village where you have lived, bring your National Health Insurance Card to the public office where you have lived before you move and report the date of your removal. Within 14 days after your move, report your move into the city, ward, town or village to the public office of your new residence.
(3) When a child is born, when the head of the family (householder) changes, or when there is a death
(4) When the insurance card is soiled, etc.
(5) When withdrawing from (leave) the system
You cannot withdraw from the National Health Insurance except for the following reasons: entering the social insurance system, moving from your city, ward, town or village.
If you withdraw from the National Health Insurance during the fiscal year, insurance premiums will be recalculated and must be paid accordingly.

Note that the documents required to present will vary depending on the circumstances.

People who cannot join the National Health Insurance
(1) People who have not registered as aliens
(2) People who do not have a status of residence (zairyu shikaku)
(3) People on short stays (in Japan)
(4) People who have already joined another health insurance system
(5) People receiving social welfare

Note 1 For details, ask a person who understands Japanese to enquire for you at your city, ward, town or village office, social insurance office or health insurance association.
Note 2 The information given is that confirmed as of July 2002. Note that a new system or system revisions may have been introduced after this date.

This information is from the CLAIR website. The Council of Local Authorities for International Relations (CLAIR) was established in July 1988 in response to rising concerns about local level internationalization in Japan.