A tire condition monitoring apparatus that improves data communication accuracy. Permanent magnets are fixed to the wheel well. A transmitter fixed to a tire includes a pressure sensor for detecting the air pressure of the tire and an MI sensor for detecting magnetic fields generated by the permanent magnets. As the tire rotates, the positions of the permanent magnets relative to the MI sensor change. Thus, the intensity of the magnetic field acting on the MI sensor changes. The transmitter determines the rotation angle of the tire based on the detection of the MI sensor. When the rotation angle of the tire is in a range optimal for wireless communication, the transmitter transmits the air pressure data generated by the pressure sensor.