When a boom cylinder (11) and an arm cylinder (18) are to be actuated simultaneously, the arm cylinder (18) is actuated after the boom cylinder (11) is actuated. A pressure reducing valve (30) is provided on a circuit which connects a hydraulic pilot valve (13) for an arm and a first pressure receiving section (16) of an arm operating valve (4) to each other. A throttle (40) and an accumulator (41) are provided on a circuit (23) connected to an output circuit of a hydraulic pilot valve (5) for a boom. The pressure reducing valve (30) is reduced in pressure by a pressure difference across the throttle (40). Thus a pressure oil flows to the accumulator (41) to produce a pressure difference across the throttle (40), so that the pressure reducing valve (30) is reduced in pressure until the pressure oil fills up the accumulator (41), and the arm operating valve (4) is switchingly actuated after a boom operating valve (3) has been switched.
