Abstract: A speed command value X1 for a first arm 3 is decided depending on a lever input amount in the direction c, d. Assuming that the side d corresponding to move-up of the first arm is positive, the side c corresponding to move-down thereof is negative, and a speed command value resulted upon full lever operation and corresponding to a rated speed of the first arm is 1, X1 is given by -1<X1<1. A speed command value X3 for a third arm 5 is decided depending on a lever input amount in the direction e, f. Assuming that the side f corresponding to dumping of the third arm is positive, the side e corresponding to crowding thereof is negative, and a speed command value resulted upon full lever operation and corresponding to a rated speed of the third arm is 1, X3 is given by -1<X3<1. A speed command value X2 for a second arm 4 is here given by X2=K1.times.X1+K3.times.X3 on condition that the side corresponding to move-up of the second arm is positive.

Abstract: Two control lever units 11, 12 for operating a first arm 3, a second arm 4 and a third arm 5 of a 3-articulation work front 2 are provided, and signals 132, 133 from the two control lever units are sent to a controller 131. On condition that a virtual 2-articulation type work front comprising a virtual first arm 13 and a virtual second arm 14 is imaginarily provided and the relationship in movement between the virtual second arm and the actual third arm is set in advance as if both the arms constitute a rigid body together, the controller 131 determines respective command values .omega..sub.1, .omega..sub.2 and .omega..sub.