PURPOSE: To suppress the hunting and realizing the control even when the difference between the target value and the current value is large by setting the auxiliary target value between the target value and the current value to realize the stabilization by the auxiliary target value even when the difference between the target value and the current value is large.

CONSTITUTION: A controlled variable data detecting means 4 is a pressure sensor to generate the electric signal E according to the pressure, and detects the current pump discharge pressure H by the pressure sensor 4, and inputs the electric signal E in the microcomputer to compare the current pump discharge pressure H with the target control value H0. For example, if the pump discharge pressure H is smaller than the target pressure H0, the pressure of the pump discharge pressure H added by the pressure value α which is stored in the memory of the microcomputer is set as the auxiliary target pressure H0'. This constitution suppresses the hunting in controlling the variable speed pump and allows the control to the target value.