A contactless power supply system for transferring power without contact between a primary side coil and a secondary side coil is provided. In the contactless power supply system, a manipulation unit manipulates a secondary side converter so that power outputted to a load is controlled to be a command value. The manipulation unit manipulates an input voltage of a primary side resonance circuit so that a current flowing in the primary side resonance circuit equals a product of a current flowing in the secondary side resonance circuit and a current coefficient. The current coefficient is defined as a square root of a specific value and the specific value is an equivalent resistance of the secondary side resonance circuit divided by an equivalent resistance of the primary side resonance circuit.