An opening and closing apparatus with a lock that is provided is capable of safely and promptly closing a sliding door, and also easily performing unlocking with a simple configuration. In an opening and closing apparatus with a lock for opening and closing sliding doors that are provided with elastic members at their door leading ends, output of an electric motor is transmitted to a rack-and-pinion mechanism or a lock mechanism. A control unit controls the electric motor such that a closing operation is performed, the closing operation operates the rack-and-pinion mechanism so as to move the sliding doors to a fully closed position and then displacing a link mechanism in a lock mechanism from an unlocking position to a locking position. Furthermore, the control unit controls the electric motor so as to reduce the output of the electric motor at a predetermined intermediate time point during the closing operation.