In a tire monitoring system for sufficiently reducing the possibility of cross talk generation of a request signal individually transmitted from a vehicle body side controller to each sensor unit, a vehicle body side antenna for transmitting the request signal and a tire side antenna for receiving the request signal are set to a coil antenna. The vehicle body side antenna is arranged above each tire such that a coil axis of the tire side antenna is set to be parallel to a rotating axis of each of tires, and a coil axis of the vehicle body side antenna is inclined with respect to the rotating axis. An inclination direction of the coil axis of the vehicle body side antenna is set so as to incline the coil axis of the vehicle body side antenna on a transversal outside of the vehicle toward a downward direction.