A power conditioner includes a PV converter that generates an output voltage, which is obtained by boosting a direct-current voltage input from a solar panel, an inverter that converts the output voltage of the PV converter into an alternating-current voltage, and a first relay connected between the inverter and a commercial power system. A controller includes a control circuit that controls the entire power conditioner, a control circuit that controls the PV converter, and a control circuit that controls the inverter. In a start process, the control circuit controls activation and deactivation of a DC-DC converter and causes the impedance of a DC-DC converter to change. The control circuit detects an input voltage and an input current of the PV converter and determines whether or not the first relay is to be in a close state according to those values.