An antenna unit having an antenna coil pattern is disposed in a casing. A sensor unit has a surface acoustic wave detecting element including a first sensing electrode that generates and receives a surface acoustic wave and a first reflector that reflects the surface acoustic wave, which are provided on a substrate configured of a piezoelectric material, and a sensor coil pattern electrically connected to the first sensing electrode and coupled to the antenna coil pattern. The sensor unit is disposed in a pressure receiving portion, and a signal is transmitted between the sensor unit and the antenna unit by wireless communication resulting from a coil coupling.