Tire condition monitoring apparatus

A transmitter has a tire condition sensor (30), a transmission circuit (35), a voltage sensor (31) and an electricity control circuit (34). The tire condition sensor detects the condition of a tire. The voltage sensor detects a voltage of the battery. During a period from when the tire condition sensor detects the condition of the tire to when the transmission circuit starts transmitting the data, the electricity control circuit performs a transmission preparation process to gradually increase electricity supplied to the transmission circuit from a battery, thereby gradually increasing a radio wave output of the transmission circuit. If the value of the voltage detected by the voltage sensor is lowered to a lowest operation voltage of the transmitter during the transmission preparation process, the electricity control circuit limits the supply of electricity to the transmission circuit from the battery.