The utility model relates to a self-checking circuit for switch quantity output, which solves the problem of difficulty in judging whether the switch quantity output is in normal operation. A self-checking unit is additionally arranged in the self-checking circuit for the switch quantity output disclosed by the utility model, and a self-checking optocoupler element is adopted to isolate a weak-current device from a strong-current device because a controller belongs to the weak-current device and a relay belongs to the strong-current device; open channels are energized by the controller and are then in loop connection with the relay, a photosensitive diode at the primary side of the self-checking optocoupler illuminates and then the secondary side is energized, and a fault condition of a relay circuit can be judged by monitoring an electrical level of a detection port connected with the secondary side. The additionally-provided self-checking unit has a simple structure, is easy to realize, and can be used for sensitively detecting whether an output channel is in normal operation.