[blimp]

multiple entry visas and multiple re-entry permits are two different things. if you have a multiple re-entry permit or a valid single re-entry permit, you don't need to do anything. however pls check to make sure that your visa doesn't say "multiple entry visa". a "multiple re-entry visa" i have never heard of.

in practise you need a re-entry permit if you wish to leave japan and come back with the same status (provided this is anything else but a short-term visitors' visa (短期滞在）. you get a re-entry permit from the immigration authorities, for instance in shinagawa, tokyo or an immigraiton office in your region. 4,000 yen for a single re-entry permit or 6,000 yen for a multiple re-entry permit. re-entry permit is called 入国許可）　(nyukoku kyoka)

now, and this is not very well known, not even to the authorities themselves. several countries have bilateral visa-agreements with japan explicitly stating that the visa shall be valid throughout the period without any additional permits. you will still have to give up your alien registration card, but in theory immigration officers shall not annul or nullify your visa. i've managed this once and failed once. had to get an emergency re-entry permit.

so why do the japanese have a visa called re-entry visa if you need to get an additional permit? excellent question. contact the US embassy or the EU delegation here in japan and I am sure that they will be just as frustrated as all the other foreigners in japan. however japan call this a service so we don't need to get a new visa every time we leave japan.