A digital output circuit to be driven by an insulated power-supply circuit includes a transistor to turn on/off an external power supply in accordance with a signal output by a light receiving element in an insulating circuit in response to a signal processed by a controller. The external supply is connected to an output device. The output circuit includes a switching unit having first and second mechanisms to switch each of wires between a connected state and a non-connected state at two places between the light receiving element and the source or emitter of the transistor, and a logic adjusting unit to adjust inversion of a logic output of the light receiving element in correspondence to the type of the transistor, such that the output circuit is switched between a sink-current type and a source-current type.

A digital output circuit to be driven by an insulated power-supply circuit includes a transistor to turn on/off an external power supply in accordance with a signal output by a light receiving element in an insulating circuit in response to a signal processed by a controller. The external supply is connected to an output device. The output circuit includes a switching unit having first and second mechanisms to switch each of wires between a connected state and a non-connected state at two places between the light receiving element and the source or emitter of the transistor, and a logic adjusting unit to adjust inversion of a logic output of the light receiving element in correspondence to the type of the transistor, such that the output circuit is switched between a sink-current type and a source-current type.