A control signal generator circuit generates control signal for changing the speed, depending on the service condition detected for every control period. When control signal generator circuit generates abnormal control signal, a condition reset controller resets the clutch to normal condition, based on the normal newest control signal stored in a SRAM. The meshing of the input and output gears are operated through a synchronizer connected to the shaft. The synchronizer is operated selectively to control the clutch during speed change. A control signal generator for the clutch control by the synchronizer generates signals based on the detected and updated service conditions of every control period.
