To control hydraulic valve even at failure of a position detecting means by providing the position control means of a spool based on the output signal of a position setting means, and a failure judging means for the position control means of the spool based on the output signals of the position setting means and a position detecting means, and the position detecting means.

In judging to failure of a position detector 3 based on the output of a damage diagnosis apparatus 8, the signal of a zero signal setter 11 is selected by a signal selector 10 to cut the feedback control computation signal based on the output signals of a position setter 5 and the position detector 3. Corresponding to the spring force of a spring 1b generated according to the operation quantity of the spool 1a of a direction control valve 1 based on only the signal of the position setter 5, the position of the spool 1a of the direction control valve 1 is controlled by feed forward signal setters 9a, 9b outputting pilot pressure oil. Consequently, even at damage of the position detector 3, the direction control valve 1 can be controlled, although the accuracy of position control is interior in the case.