To provide a transmitter and a receiver where the receiver can avoid reception of other undesired radio waves when the receiver receives a radio wave transmitted from the transmitter.

The transmitter is provided with a sensor and a radio wave transmitter. When the sensor senses a fault, the radio wave transmitter transmits a fact of the sensing in a form of a signal wave. A reception device of the receiver is placed in a circuit A, and a reception device receiving the radio waves other than a signal radio wave from the transmitter is placed in a circuit B. A display device displaying the operation of the circuits A, B is provided in a circuit C in this receiver.