A control device is a control device of a power conversion device, and includes a conversion value calculation unit that acquires a current value of a current flowing in an alternating-current capacitor connected to a capacitor circuit in an output circuit on an alternating-current side of an inverter circuit and performs conversion of the current value to obtain a predetermined conversion value, and a failure detection unit that compares the conversion value obtained by the conversion value calculation unit and a predetermined determination value to be used in failure detection to detect a failure of the alternating-current capacitor.