To supervise the malfunctions of a servo valve, in a servo valve control that gives command for the spool travel of the servo valve by performing a proportional control and an integral control with the input of a deviation between a control command, previously given as a set point for an object to be controlled by the servo valve, and a control result feedback from the object.

Working fluid temperature of a servo valve and the ambient temperature around the servo valve are measured. The command for the spool travel of the servo valve is compensated, based on the measured working fluid temperature and the measured ambient temperature. Accordingly, while performing servo valve control, based on the compensated spool travel command, this servo valve control supervises the malfunctions of the servo valve by monitoring the control input of the integral control.