PROBLEM TO BE SOLVED: To enable power transmission control so as not to affect foreign matter.SOLUTION: The power transmission device includes: communication means for communicating with an electronic device; power transmission means for wirelessly supplying power to the electronic device; and control means for controlling the communication means and the power transmission means. The control means starts power transmission by the power transmission means after communication by the communication means, and thereafter, alternately performs communication by the communication means and power transmission by the power transmission means. The communication power by the communication means, the power transmission power by the power transmission means, the length of the communication period and the length of the power transmission period are adjusted through a communication period of communication by the communication means and a power transmission period of power transmission by the power transmission means, so that an average magnetic field intensity does not exceed a first magnetic field intensity within the predetermined region, and a maximum magnetic field intensity does not exceed a second magnetic field intensity within the predetermined region.SELECTED DRAWING: Figure 2