PURPOSE: To reduce engagement shock by detecting an oil rate supplied to a transmission clutch from the time of switching to a running range, and controlling the oil rate supplied to the transmission clutch when the detection oil rate is a specified value or more.

CONSTITUTION: Oil is discharged from a pump, and adjusted in its pressure to be a specified operation pressure through a regulator. It passes an operation oil passage 1, and supplied to a transmission clutch 4 through a manual valve 2 and an opening area variable device 3. A position of a shift lever 5 is detected by a shift lever position detection device 6. When the manual valve 2 is moved to an N range to a D range, an oil rate supplied to the clutch 4 is computed by an oil rate computing device 7. The opening area variable device 3 is controlled by means of the opening area control device 8 as an oil supply rate control means according to the rate computed by the oil rate computing device 7. The oil rate to be supplied to the transmission clutch is properly controlled, so that engagement shock of the clutch 4 is reduced.