To provide a locking device for power slide door capable of giving a user a notification that a power slide door being an object of locking reservation is not locked when the power slide door is not locked because the power slide door has not been closed due to any abnormality after the locking reservation was performed during closing operation of the power slide door.

A locking device for a power slide door is equipped with a power slide door ECU 21 for determining an abnormal state of a power slide door which has been in closing operation and is not in its closed state after a Smart ECU 11 receives a locking reservation. The locking device is equipped with a body ECU 31 which outputs a ringing signal and a blinking signal both notifying that a slide door body is not locked when the power slide door ECU 21 determines an abnormal state.