Apparatus for controlling the boom-swing combined motion of an excavator

A hydraulic control device includes first and second pumps, a swing control spool (13), a boom first-speed control spool (11A), a boom second-speed control spool (11B), a swing motor (1), a boom cylinder (3), a pilot control valve (24), and a confluence line (25) for merging the hydraulic flow from the boom second-speed control spool with that from the boom first-speed control spool. Provided on the confluence line is a swing priority valve (30) having an orifice (31) for variably reducing the hydraulic flow supplied to the boom cylinder through the confluence line. A swing priority control line (27) is provided to interconnect a pressure receiving part of the swing priority valve and a swing control pilot pressure signal line of the pilot control valve in such a manner that an aperture area of the variable orifice of the swing priority valve (30) is reduced in proportion to the magnitude of a swing control pilot pressure of the pilot control valve (24).