Electric power transmission device and electric power transmission system

One aspect of the present invention is an electric power transmission device that periodically shifts a frequency of a magnetic field to a plurality of predetermined shift values and that transmits electric power by utilizing the magnetic field. The device includes a plurality of power transmitters and an instructor. Each of the plurality of power transmitters configured to generate a magnetic field. The instructor outputs an instruction signal indicating a shift value to be shifted to each of the power transmitters to instruct the shift value to be shifted to each of the power transmitters. Further, the instructor instructs the shift value to be shifted in such a manner that at least a part of the magnetic fields of the plurality of power transmitters are different in frequency at the same time point.