A charging device to wirelessly charge a target device, including: a coil antenna having a first surface facing a first direction at which the target device is placed for charging and a second surface facing an opposite direction from the first direction, generating a first magnetic field; a plurality of pairs of metallic small loop transmission coils arranged to the second surface side of the coil antenna, to generate a second magnetic field in response to the first magnetic field to enhance the first magnetic field, the first and second magnetic fields being directed in the first direction; and wherein a first one of each pair of metallic small loop transmission coils is coupled to a second one of the pair in parallel and a size of the first one of each pair is different from that of the second one of the pair, such that when a distance between the target device and the first surface is changed, one of the pair of metallic small loop transmission coils is enabled to be resonant with the coil antenna.