Until now, it was National Health Insurance, but I joined the workplace employee health insurance. Do I need to apply for National Health Insurance?

You will need to apply for the loss of National Health Insurance qualification.
Please notify Insurance and Pension Division National Health Insurance Section of your ward office within 14 days.
If all members of the National Health Insurance of the household change to the workplace employee health insurance, the insurance premium will be settled upon notification.
In addition, if it is difficult to visit the ward office Hours due to employment, etc., we will also accept notification by mail. If you wish to apply by mail, you can download registration form from our website. If you are unable to use the Internet, please contact your ward office Insurance and Pension Division National Health Insurance Section by phone.

Insurance and Pension Division National Health Insurance Section, ward office in your ward
　

・New workplace insurance card (insurance card for all those who stop National Health Insurance)
・Your National Health Insurance Insured Card
・Identity verification documents (My number card, license, passport, etc.) of the person to be notified

What is necessary for the procedure (don't forget to report in such a case)
About notification of loss of National Health Insurance qualification by mail
Contact (Ward Office Insurance and Pension Division)
Procedures for National Health Insurance by Mail