A tire monitor radio circuit includes a control circuit delivering a binary digital baseband signal, a modulation circuit having an oscillation circuit generating a carrier wave and switched between an oscillatory and a non-oscillatory states, an antenna resonance circuit having a coil and a capacitor both connected together, a resistance damping circuit having a switching element and a resistance and connected to the antenna resonance circuit, the resistance damping circuit being switchable between an operative and an inoperative states, and a compensation circuit putting the resistance damping circuit into the operative state when the modulation circuit is switched to the non-oscillatory state, the compensation circuit returning the resistance damping circuit to the non-operative state when or before the modulation circuit has been or is switched to the oscillatory state. When he resistance damping circuit is on the operative state, resonance current of the damped oscillation in the antenna resonance circuit is applied to the resistance, and the resistance serves as a damper thereby to reduce statically determinate time of damped oscillation. As a result, the digital signal can accurately be detected from the carrier wave at the reception side. Consequently, reliability in the communication can be improved.