To make it possible to update process data automatically even during plant operation without influencing control during operation thereof.

A controller is configured redundantly and each controller 11 is provided with a level converting section 19 which converts a valve position signal S4 of a control valve 2 into a given signal level and output it as the valve position signal S5, and are also provided with a valve opening indicating section 22 which computes and outputs the valve opening for specifying a flow rate of a control valve 2, a valve position control section 25 which outputs a valve position control signal S8 so that a signal showing an opening of a present control valve 2 from the level converting section 19 and a signal from the valve opening indicating section 22 of a targeted control are matched with, a set point updating section 28 which obtains process data in the level converting section 19 and performs updates of the data, a control separating section 33 whereby control is not influenced by a signal from the valve position controller 25 when the set point updating section 28 is updating data from the level converting section 19.