System is provided for controlling the pressure with which a clutch is engaged, with a slip rate e of the clutch, which is equal to the ratio of the rotational speed of a drive shaft thereof, as a main parameter. A microprocessor reads a throttle opening and the slip rate e from the initiation of engagement of the clutch at a time interval of 0.4 sec, and accesses a particular group of controlling data which control the clutch engagement and which are grouped together as a function of a time lapse l as well as the read values of these parameters. During the interval of 0.4 sec, the microprocessor sequentially outputs the controlling data of the particular group with a time subinterval of 0.05 sec. The time interval includes subintervals corresponding to l=0 to l=8 at maximum, from the initiation to the completion of the clutch engagement. Each subinterval l=0 to l=8 spans 0.4 sec. When a temporary clutch activation is instructed, the microprocessor changes the length of the subinterval from 0.05 to 0.1 sec, and also changes the time interval l to 0.8 sec. When the slip rate e is low at the initiation of the clutch engagement, a group of controlling data is selected which is to be assigned to a first subinterval l=0 corresponding to the deceleration of the clutch drive shaft.