Provided is an inspection device that can determine by itself whether a power-supply-side circuit (11, 22, 23) including a solar-cell string (11) is electrically isolated from a PCS (13, 130). The inspection device (14, 140) measures the impedance of the power-supply-side circuit including the solar-cell string (11) and determines whether the power-supply-side circuit is electrically isolated from the PCS (13, 130) on the basis of the capacitive component of the measured impedance.