PURPOSE: To shorten a cycle time, by providing a push-in member driving means, the stroke position detector of the push-in member, a push-in force detector and a control means which controls the driving means.

CONSTITUTION: A control means 17 controls a driving means 12 so that the moving speed of a push-in member 6a becomes constant at the stage of a push-in force being unnecessary in a series of push-in processes. When it is detected by a position detector 16 that the push-in member 6a reaches the stage necessary for the push-in force, the control means 17 controls the driving means 12 so that the push-in force of the push-in member 6a becomes in a desired constant size based on the push-in force information fed from a push-in force detector 15. Also when it is detected by the position detector 16 that a failure is generated in push-in in the case of the size of the push-in force being comparatively small, the control means 17 controls the driving means 12 so that the push-in member 6a performs a re-push-in with the push-in force smaller than the size of the previous time push-in force. Consequently a cycle time can be shortened.