The present disclosure relates to a wireless power transmitter device, a wireless power receiver device, and a system for transferring power wirelessly. A wireless power transmitter device according to an embodiment of the present disclosure can include: a driving coil configured to transmit power wirelessly; a magnetic coupler mutually inductively coupled with the driving coil; and a resonance frequency adjuster part configured to adjust the resonance frequency of the magnetic coupler, where the magnetic coupler can include a plurality of coils arranged in a region opposite one side of the driving coil.