Thanks for your answer ...
I was pretty sure it was not possible but, i gave it a try on this forum ...
It's sad i can't do anything, this watch is a really great one. It's my second G-Shock and i'm found of it (my first one is one of the first model, all in green plastic and still working after more than 10 years of shocks !!!) but i would have prefered to know it was not a world wide atomic watch before buying it instead of what, the seller told me it works in europe ... So if anyone want to buy a watch in Japan without speaking japanese, take care about Yodobaishi Camera's sellers ...