To control a tire inflation pressure during running as well as before and after running to obtain an optimum pressure by attaching a gas cartridge filled with carbon dioxide gas, nitrogen gas or air and a small sized pressure reducing valve (regulator) to a bicycle tire.

This tire inflation pressure retaining device for bicycle has a pressure reducing valve, a cartridge 2 and a holding device. The pressure reducing valve is provided with a mounting port 11 for a tire valve v at one axial end and a mounting port 12 for the cartridge 2 at the other end. Both mounting ports 11, 12 are communicated through a pressure reducing part 13 and a check valve 14. The cartridge 2 contains a pressurized gas encapsulated by a sealing part 21. A holding means holds the cartridge 2 to spokes on both side of the cartridge 2.