PURPOSE: To prevent swing-back on the occasion of intermediate stop without resorting to a mechanical brake and stop a feed bar quickly by releasing the air pressure in an air cylinder on the reverse drive side to an air cylinder on the forward drive side immediately before the feed bar stops.

CONSTITUTION: An opening/shutting valve 16 is installed in a pneumatic circuit 15 connecting air pressure supply/exhaust circuits 9, 8 with each other, which are connected with two supply/exhaust ports 1a, 1b of a swing type air cylinder 1. The speed of a feed bar 3 to transport a work 4 is sensed, and a programmable controller 14 judges whether the moving speed of the feed bar 3 has dropped to a specified value around zero. If yes, the opening/shutting valve 16 is opened to put the circuits 8, 9 in communication with each other. Thereby the air pressure in the air cylinder unit on the reverse drive side of this swing type air cylinder 1 is released to the other air cylinder unit on the forward drive side, and thus the air pressures in these air cylinder units are put in equilibrium.