An end of a hollow member is connected to an air valve for introducing air into a tire. A detecting and transmitting unit for detecting an air pressure in the tire and transmitting pressure information out of the detecting and transmitting unit is connected to an opposite end of the hollow member. A detecting and transmitting unit is mounted on a hub of a wheel portion. The positioning of the detecting and transmitting unit minimizes any deviation from the dynamic balancing of the wheel. Consequently, the air pressure detecting device for a wheel can be subsequently installed on the vehicle.