An expression shoe includes a pedal, a base, and a bearing arrangement rotatably connecting the pedal to the base. The frequency adjustment section is configured to adjust a transmitting frequency at which the detected value of the tire air pressure detected by the air pressure detecting unit is externally transmitted by the transmitting unit according to the running state detected by the running state detecting unit and the air pressure change rate detected by the air pressure change rate detecting section. The substrate includes a second contact.