A wireless sensor system of the present invention includes wireless sensor units (4A, 4B) and a sensor signal receiving unit (5). The sensor units (4A, 4B) have sensors (6A, 6B), an electric power receiver (8A, 8B) for securing the electric power from an electromagnetic wave of a power feeding frequency f1 through a tuning circuit and a detecting and rectifying circuit, and sensor signal transmitters (9A, 9B) for transmitting the signals outputted from the sensors as a wireless sensor signal of the electromagnetic wave of unique frequencies f2 and f3 different from the power feeding frequency f1. The sensor signal receiving unit (5) has an electric power transmitter (12) for transmitting the electromagnetic wave of the power feeding frequency f1 to the units (4A, 4B) and a sensor signal receiver (13) for receiving wireless the sensor signals of the respective frequencies f2 and f3 transmitted from the units (4A, 4B).