either of left and right directions by the pilot pressures provided from the pilot valve 13 b so that it can supply hydraulic flow for boom low speed actuation to the boom cylinders 15 no description will be offered regarding the arm low speed control valve 18 a and the arm high speed control valve 18 a in light of the fact that they play no meaningful role in the hydraulic control device of an excavator of the present invention outlet ports of the boom high speed control valve 7 and the boom low speed control valve 11 are connected through a confluence line 9 the hydraulic flow of the first hydraulic pump 1 through the boom high speed control valve 7 and the hydraulic flow of the second hydraulic pump 2 through the boom low speed control valve 11 are confluent together and supplied to piston side chambers 15 a 15 b of the boom cylinders 15 through the confluence line 9 a swing priority valve 20 is provided on the pressured fluid supply line 8 for delivering the flow rate of the first hydraulic pump 1 to the boom high speed control valve 7 the swing priority valve 20 throttles the pressured fluid supply line 8 by a swing priority pilot pressure so as to reduce the flow rate of the first hydraulic pump 1 to the boom cylinders 15 thereby relatively increasing the flow rate of the first hydraulic pump 1 supplied to the swing motor 14 the swing priority valve 20 has an orifice 20 a for throttling the pressured fluid supply line 8 and.