Hi I am French citizen living in Japan. I am going to France by China. Do I need a transit visa?

If you transit Shanghai, a transit visa is not required for less than 48 hours stopover and you can leave the airport. If you transit other city in China, a transit is not required for less than 24 hours stopover and you can't leave the airport. If you really want to go to visit the city, you can try to apply for a 24 hour stay permit when you arrive.