Permission to work in Japan
When you are in a foreign country, your visa determines what you can do. A work visa allows you to work, a student visa to study, and so on. If you have a short-stay (or tourist) visa, then you are a tourist and thus cannot work, or (theoretically) study - although in fact for short-term studies of up to 3 months, this is the most common visa. Japanese Consulates almost exclusively issue the short-stay (tourist) visa for studies except in the case of certain nationalities without formal visa exchange agreements with Japan where it is necessary to have a student visa even for short-term studies (in particular it takes time for Vietnamese, Mongolian and nationals of many former Soviet states to get confirmation of visa applications).
Tourist visa
You cannot take paid work in Japan on a short-stay (tourist) visa. However, you may work provided you are not in any way paid for that work.
Work visa
Your visa allows you to undertake certain paid activities depending on the class of visa issued to you. There are limitations: you must receive at least the same salary as a Japanese person doing the same job would receive (to prevent cheap labour being imported by companies and taking work from equally qualified Japanese workers). The main categories of work visa are detailed on the work visa page.
Student visas
You cannot work on your initial visa, but you can apply for a document entitled "Permission to engage in an activity other than that permitted by the status of residence previously granted." This just means permission to work up to 4 hours per day, 28 hours per week, in order to help support your studies. During holidays, you may work up to 8 hours per day. However, this is intended to be supplemental to your savings, so you cannot declare this proposed income when applying for a student visa. Also, this activity is not meant to detract from your studies - so if your attendance begins to suffer as a result of working you may find your visa revoked. The immigration office does check your attendance while on the student visa, and the school is obliged to take a daily record of attendance.
The relevant forms for application are usually available from your school. Some schools will make the application for you; most will just issue you with the documents that you need to take to the immigration office.
Other visas
Permanent Residents, Spouse or Child of a Japanese National, Spouse or Child of a Permanent Resident, and Long-term Residents are all able to work without restriction in Japan. Other visas such as cultural activities do not allow you to work or to apply for permission to work. If in doubt, contact us with details of your visa and present situation, or contact the immigration office directly.