A control system for an automatic transmission includes: an input clutch applied, responsive to selection of a forward running range, to transmit the rotation of an engine to a transmission mechanism; a hydraulic servo for selectively applying/releasing the input clutch; a stop state detector for detecting a stop state of a vehicle in terms of the selection of the forward running range, lack of vehicle speed, the release of an accelerator pedal and the depression of a brake pedal; starting operation detector for detecting an operation to start the vehicle in motion; application state detector for detecting the application state of the input clutch; and a controller for controlling oil pressure fed to the hydraulic servo on the basis of signals coming from the various detectors. If arrival at a predetermined released state is decided, the hydraulic servo is fed with a summed oil pressure which is the total of an initial application oil pressure and a release oil pressure, to initiate piston movement and start of engagement of the input clutch, and the oil pressure is thereafter gradually raised from the summed pressure on the basis of a predetermined pressure relationship. If a failure to arrive at the predetermined released state is decided, the oil pressure is gradually raised on the basis of the predetermined pressure relationship from the oil pressure which is fed to the hydraulic servo when a starting operation is detected.