PURPOSE: To furnish a sensor to easily detect opening and closing a diaphragm valve and to carry out transmission of an electric operation signal to control opening and closing the diaphragm valve and transmission of a confirmation signal of the actuation state of the diaphragm valve with a pair of electric lines.

CONSTITUTION: A valve control device is constituted of a coil 11 used for a pilot valve of a diaphragm valve, a switch 18 to switch on and off positive and negative direct currents to the coil 11, electric contact points B, A for a confirmation signal of opening and closing of the diaphragm valve, a diode 17 to prevent closing and opening signals of a valve at the time of opening and closing the valve, a means 11 to detect electrification of the coil 11, etc. When an ON button of the switch 18 is switched on for a period of t0 an electric current of a continuous line arrow flows to the coil 11, the diaphragm valve comes to be open after t1, the electric contact point B opens and the electric contact point A closes. Consequently, the electric current of the continuous line arrow becomes zero, and it is possible to detect an opening state of the diaphragm valve by a detection means 19.