Charging device, power receiving device, and method

Attenuation of transmission power transmitted from a power transmission coil according to distance causes a problem that a power receiving device such as a smartphone with an accessory cover may increase a difference from reception power received by a power reception coil and prevent normal charging. Therefore, provided is a charging device including, for example, a transmission unit that periodically transmits a response request, a reception unit that receives a response to the response request from a power receiving device, a determination unit that determines whether a power intensity of the response request received by the power receiving device, indicated by the response, is equal to or less than a predetermined threshold, and a power control unit that increases output power of the response request when it is determined that the power intensity is equal to or less than the predetermined threshold.