To provide a wireless sensor system, in which an abnormal power supply in the power supply section can be ascertained, for avoiding a malfunction of the system and accomplishing a stable power supply with reduction of the consumption of a power being transmitted, the wireless sensor system includes wireless sensor units and a sensor signal receiving unit. The wireless sensor units include a sensor section for detecting a detection object, a sensor signal transmitting section for transmitting by wireless a sensor signal from the sensor section, and a power supply section having a power receiving section for receiving a driving power transmitted by wireless. In this system, a power supply monitoring section is provided for monitoring the voltage of the power supply section. The sensor signal receiving unit includes a monitor dependent power control section for regulating the power to be transmitted, depending on a monitored result of the power monitoring section.