A clutch control system for a transmission for detecting if hydraulic control during shifting is not executed. A first clutch and a second clutch are switched from a disengagement state to an engagement state by receiving a predetermined pressure generated by a hydraulic pump. A transmission executes shifting to an adjacent gear step by operation of switching the engagement state of the first clutch and of the second clutch from one side to the other side. If an elapse time t from the start of clutch switching operation reaches a predetermined time and an input-output speed ratio which is a ratio between engine speed and counter shaft rotational number falls within a predetermined range corresponding to a gear step before shifting, the transmission control unit discontinues the clutch switching operation by stopping the supply of hydraulic pressure to the other side clutch to bring it into the disengagement state.