A contactless power supply system includes a contactless power supply device and a power receiving device. Power is supplied from the contactless power supply device to the power receiving device while communication is performed therebetween. The power receiving device includes a power receiving coil unit, and a first communication unit that attaches information having continuity to data transmitted to the contactless power supply device. The contactless power supply device includes a power supply coil unit, a second communication unit, and a power supply control unit that, in a steady state where communication is performed between two communication units after the second communication unit begins receiving the data transmitted from the first communication unit, refers to information having continuity attached to the data, and if continuity has been lost, performs correction to increase the output value of the power from the power supply coil unit to the power receiving coil unit.