driver’s licence for renting a car

I'n from Belgium and I'm going to Japan for vacation. I want to rent a car but an international driver's licence issued in Belgium cannot be used in Japan. So my licence must be switched to a japanese and translated. I think this can be done in JAF-office. Has anydone done this? Is the procedure straightforward? Is it possible to arrive in Tokyo and get de licence the same day?

That's strange that Belgians can't use an international license. Did you get that from a reliable source?

I got my license translated at JAF in less than 20 minutes. It cost 3,000 yen.

From this page:
http://www.japan-guide.com/e/e2022.html

Japan recognizes only international driving permits, which are based on the Geneva Convention of 1949. A few countries, including Belgium, France, Germany and Switzerland, however, issue international driving permits, which are based on different conventions. The permits issued by those countries are not valid in Japan.

Instead, holders of a French, German or Swiss driver's license can drive in Japan for up to one year with an official Japanese translation of their driving licenses to be obtained from the respective country's embassy or consulate in Japan. People from other countries, whose international driving permits are not recognized by Japan, must attain a Japanese driving license in order to drive in Japan.

You should be able to do it at JAF.

See here: http://www.diplomatie.be/tokyo/

Do you think it's realistic to arrive at Narita apt and the same day go to a JAF-office to take the translation and than rent a car?

renting a car on a first vacation to Japan may not be the wisest thing to do. I would suggest that you get to know Japan a bit first. It is really easy to travel by train far and wide, though staying in one region only is enough, due to the culture shock. Roaming around the Kansai for example allows you to be familiar with a couple of places close to one another (I first went to Tokyo on my third trip. the first 2 and the start of the 3rd were in Kansai)

It will be my 5th trip to Japan. This time I want to visit the lesser touristed parts of this beautiful country wich are not so accesible by public transport.