PURPOSE: To eliminate the time loss for connecting clutches and shorten the cycle time by connecting the clutches during the mold closing process and starting the clamping process immediately after the completion of the mold closing process.

CONSTITUTION: A fixed platen 12 and a clamping housing 14 are disposed facing each other on a bed 10. When a movable platen is moved back to the point of completing mold opening, a motor 34 for mold opening and closing is started for starting the mold closing process. At that time, clutches 38 are released. The rotating speed of the motor 34 for mold opening and closing is sensed by a rotating speed sensor 40, and a controller 46 outputs a signal for connecting the clutches 38 by means of a comparison device 42. The connection of clutches 38 is started by said arrangement and the connection of clutches 38 is completed by the time the movable mold 22 is brought into contact with a fixed mold 20 when a molding is manufactured by cooling, a motor 36 for clamping is stopped and the clutches 38 are released.