Provided is a power unit including: a power converter circuit connected to an external power supply, the power converter circuit being configured to generate a voltage necessary to drive a driven device; a communication terminal connected to a controller, the communication terminal being configured to transmit and receive information between the controller and the driven device; a power supply control terminal connected to the controller, the power supply control terminal being applied with a direct current voltage from the controller; and a relay element provided between the external power supply and the power converter circuit, the relay element being configured to control supply of electric power to the power converter circuit, wherein the relay element is driven by a direct current voltage applied from the power supply control terminal when a power supply of the controller is turned on, and electric power is supplied to the power converter circuit.