An electric power transmission device characterized in that the electric power transmission device includes a power transmitting unit which wirelessly transmits an electric power and a power receiving unit which receives the electric power, the power transmitting unit and the power receiving unit include a coil for electric power transmission and an inclusion unit made of a dielectric material covering the coil for electric power transmission, at least one of the power transmitting unit and the power receiving unit includes an impedance adjustment unit which varies the impedance thereof, and the electric power is transmitted at a resonance frequency determined by an impedance of the power transmitting unit, an impedance of the power receiving unit, and an impedance of the conducting medium.