A battery pack for use in an electric machine, includes a first receiving antenna including a first inductor for receiving electric power from a power supply source located outside the electric machine by coupling with a first resonant magnetic field generated by the power supply source; and a transferring antenna including a second inductor for generating a second resonant magnetic field by the radio-frequency power. A primary surface of the first inductor is located within the battery pack and is parallel to a first plane of the battery pack. A primary surface of the second inductor is located within the battery pack and is parallel to a second plane of the battery pack. The second plane facing the second inductor intersects with the first plane facing the first inductor at an angle of a range of between 45° and 90° including 45° and 90°.