A vehicle body side system is provided with a second data communication unit that performs bidirectional communication with a tire side device and receives road surface data and measurement data transmitted from a first data communication unit, a road surface determination unit that determines the road surface condition of a road surface on which a vehicle travels based on the road surface data, a reception strength measurement unit that measures the reception strength of the measurement data, and a transmission angle setting unit that stores the reception strength of the measurement data during one rotation of a tire, sets as a transmission angle, a presence angle when the reception strength of the measurement data during one rotation of the tire is high, and transmits data indicating the transmission angle to the tire side device via the second data communication unit. In addition, a control unit causes the first data communication unit to transmit the road surface data when the presence angle becomes the transmission angle.