To smoothly conduct a mode selection, a switching operation and the like capable of selectively controlling an air cylinder to an automatic mode and a manual mode.

A circuit breaking valve 14 is provided on the way of air pipes 9A, 9B connecting the spacing between the air cylinder 3 and a positioner 7. A mode switching valve 21 is provided via branch pipes 16A, 16B or the like in the spacing between the air cylinder 3 and the circuit breaking valve 14. The operator manually operates the mode switching valve 21 and when the operator makes a switch from the automatic position (a) to the switching positions (b), (c), (d) in the manual mode, the pilot pressure to the circuit shutoff valve 14 is reduced to the atmospheric pressure level so that the passage between the positioner 7 and the air cylinder 3 can be shut off with the circuit shutoff valve 14. Then, auxiliary air from a hand pump 18 is supplied/exhausted to/from the air cylinder 3 via the branch pipes 16A, 16B and the air cylinder 3 is driven with the manual mode.