According to one embodiment, a wireless electric power transmission device supplies electric power, transmitted wirelessly from a first device, to a load circuit. The device includes a power receiving resonance unit, a detecting unit which detects electric power information corresponding to the electric power supplied to the load circuit, and a control unit. The control unit determines whether to adjust at least one of a resonant frequency of the power receiving resonance unit, an output frequency of an alternating current power supply of the first device, and a resonant frequency of a power transmitting resonance unit of the first device, on the basis of a relationship in terms of magnitude between first electric power information when the impedance is a first impedance and second electric power information when the impedance is a second impedance.