A non-contact power supply system includes a power supply device for transmitting high frequency power and a load device which receives the high frequency power in a non-contact mode by electromagnetic induction to supply it to a load. The power supply device includes a power transmission unit having a primary power coil and an inverter circuit, an inquiry unit having at least one primary signal coil and an oscillation circuit, a signal detection unit and a control unit. The load device includes a power reception unit having a secondary power coil magnetically coupled to the primary power coil and a power conversion unit, a secondary signal coil magnetically coupled to the primary signal coil, and a response unit which is operated by electromotive force induced in the secondary signal coil. The control unit stops power transmission when no signal is detected and executes power transmission which a signal is detected.