A system for controlling an automobile transmission effects a gear change by disengaging synchronizing clutch means for a present gear position, achieving a neutral gear position, and then engaging a synchronizing clutch for a next gear position in response to a shift control signal. The automobile transmission has an actuator for selectively engaging and disengaging the synchronizing clutch. An electronic control unit controls an engine output adjusting assembly to adjust the output power of the engine and also controls the actuator to start disengaging the synchronizing clutch for a present gear position in response to a shift command signal. The electronic control unit also controls the actuator to complete disengaging the synchronizing clutch for a present gear position to enter the neutral gear position when substantially no load is transmitted between drive and driven members of the synchronizing clutch for a present gear position under the control of the engine output adjusting assembly.