PURPOSE: To set a desired predetermined valve opening degree with a high degree of accuracy by transmitting a control signal having a desired control value to a valve drive section from an operation section so that the valve drive section controls the valve opening degree in such a way the opening degree of a valve coincides with the desired control value.

CONSTITUTION: When an open position on a touch control section 12 is touched, an open control signal 12a-In is delivered to a desired control valve generating means 13 from which a desired control value SV as an output is continuously increased in the time of the above-mentioned input, and is displayed on a CRT display section 12. When the above-mentioned displayed value comes to the desired control value SV, the increase of the desired control value SV is stopped if the above-mentioned touch is stopped. Meanwhile, a desired control value SV which is transmitted from a CRT operation section 11 to a valve drive section 17 arrives with a delay corresponding to a processing time in a data transmission section 16. In accordance with the desired control value SV, the valve drive section 17 delivers an increasing pulse 17-In, and delivers a decreasing pulse 17b-De to an inching valve 18 just before the valve opening degree PV comes to the desired control value SV. Accordingly, the overshooting of the valve opening degree PV is remedied, thereby the valve opening degree is set to a predetermined value.