[Sangetsu]

No quarantine is necessary if you can prove your dog has had 2 rabies vaccinations within a 12 month period (i.e. a shot in January, and a second shot in November or December of the same year). Without proper vaccinations, your dog will be held in quarantine at your expense.

Most larger apartment buildings do allow pets, but they usually limit them to "medium" size. However, no one really knows what "medium" is exactly, and I see a great many Labradors, Retrievers, and such being walked around the city.

Your apartment building will require that your dog be registered with the local ward office, who will check to make sure that your dog is properly vaccinated. You'll also be given a sticker to put on your front door to let people know that there is a dog in your apartment.

I'm in the process of bringing my 2 dogs to Japan, hopefully in early 2011. I have a house outside the city with a yard, so it's not as much of a problem for me.