POWER TRANSMISSION DEVICE AND CONTACTLESS POWER TRANSMISSION DEVICE

A power transmission device is provided that enables more accurate detection of an undesired switching state for a switching element and an appropriate supply of power. The power transmission device includes a power supply, a switching element, a ringing detection circuit, and a control circuit unit. The ringing detection circuit detects ringing that occurs in the switching element. The control circuit unit controls at least the power supply or the switching element in accordance with a detection result of the ringing detection circuit. The ringing detection circuit includes a diode and a resistor. The diode conducts when a negative polarity voltage is generated in the switching element. The resistor is connected in series with the diode.