PURPOSE: To hold the angle of a bucket with a high accuracy as well as prevent the hunting of the bucket by hastening the response of control by using a system in which the angular velocity of the bucket is controlled by the angular veloxity signal of the operating arm and its position is controlled by the deviation signal of the angular veloxity.

CONSTITUTION: When operating an operating arm, the angular velocity signals α, β, and γ of the operating arm are obtained by angle guages 8, 9, and 10, angular velocity signal γ' according to the angular velocity of the bucket is obtained from the angular velocity signals α, β and γ, and the bucket is turned by open- loop control at the angular velocity corresponding to γ. On the other hand, an angle deviation signals Δγ is obtained and control is also made on position feedback. The sum of the angular velocity control signal γ' and the angle deviation signal Δγ is output, the highest one of the oil pressure of the output and the pilot pressure of the pilot operation valve 13 is supplied to the switching valve 12 of the oil-pressure cylinder 7 of the working machine, and the valve 12 is controlled by shuttle valves 23a and 23b.