A power transmission device applies a alternating-current voltage to an active electrode OPPOSING an active electrode of a power reception device with a gap therebetween, and to a passive electrode OPPOSING a passive electrode of the power reception device with a gap therebetween and transmits power via electric field coupling. The power transmission device includes a controller that monitors a voltage applied to the passive electrode. If a change in the voltage per unit time exceeds a threshold, the controller determines that a metal foreign object has become interposed between the active electrodes and a user has touched the metal foreign object, and stops the transmission of power to the power reception device. Thus, a power transmission device and a wireless power transmission system are provided that are capable of preventing with certainty a malfunction due to a foreign object when a foreign object has become interposed between electrodes.