Tire condition monitoring with temperature dependent transmission times for higher reception probability

A transmission controller (31) for a transmitter (34) compares the value of data of the temperature in a tire measured by a temperature sensor (33) with a predetermined threshold temperature, and determines the number of times a transmitting circuit performs the transmitting operation in a cycle of a predetermined length of time. For example, when the temperature in the tire rises, the number of times the transmitting circuit performs the transmitting operation in the predetermined cycle is increased. Therefore, the reduction in the reception probability of a receiver (40) is limited even when the transmission output of the transmitter is reduced due to temperature affect.