A terminal circuit in an inverter is disclosed, the terminal circuit including a photo-coupler configured to electrically insulate input/output signals, to receive, as input, an open collector output signal or a pulse output signal from a first port and to output the open collector output signal or the pulse output signal to a second port through a first output terminal, a transistor in which a base (B) terminal is connected to a second output terminal of the photo-coupler. And a bias resistor connected to a base (B) terminal of the transistor and to an emitter (E) terminal.