A transmitter of a tire condition monitoring apparatus has an acceleration sensor, a transmission circuit, an antenna and a transmission controller. The transmitter is provided in a tire of a vehicle. The acceleration sensor detects a running state of the vehicle. The transmission circuit generates a transmission signal containing data representing a condition of the tire and outputs the transmission signal. The antenna wirelessly transmits the transmission signal. The transmission controller changes a transmission power of the transmission circuit according to a detection result of the running state detection device. This is capable of transmitting signals with an appropriate transmission power.