Pressure sensor, transmitter, and tire condition monitoring apparatus

A pressure sensor (32) has a diaphragm (103) that is exposed to air in a tire of a vehicle. A transmitter (30) wirelessly transmits data representing the air pressure of the tire. The casing (70) accommodates the transmitter (30) and the pressure sensor (32). A lid (73) closes an opening (72) of the casing. A metal body (500) is provided on the lid. When the opening of the casing is closed with the lid (73), the diaphragm (103) is covered with the metal body (500).