Wireless power charging system

A wireless power receiving device which receives electric power wirelessly from a wireless power transmitting device, the wireless power receiving device including a reception coil unit, wherein the reception coil unit includes:

• an insulating layer;
• a first coil including a first body portion disposed as a spiral on a first surface of the insulating layer and a first lead portion extending from a first end of the first body portion and led out of the insulating layer;
• and
• a second coil including a second body portion disposed on a second surface of the insulating layer opposing the first surface and electrically connected to a second end of the first body portion through a via and a second lead portion extending from the second body portion and led out of the insulating layer,
• wherein the second coil has a width larger than that of the first coil and a thickness smaller than that of the first coil.