A contactless power supplying system, which excites a primary coil of a power supplying device to generate an induced electromotive force at a secondary coil of an appliance arranged on the device and supply the induced electromotive force to a load of the appliance, includes a metal foreign object detection device. The metal foreign object detection device includes an antenna coil, an oscillation circuit, and a detection circuit. The oscillation circuit includes a component having a design value that generates oscillation in a range of oscillation conditions from immediately after the oscillation circuit starts to generate oscillation to just before a stable and continuous oscillation condition. The detection circuit detects a suspension of the oscillation or an attenuation in amplitude of the oscillation based on a change in an electric characteristic of the antenna coil caused by a metal foreign object on the power supplying device.