PURPOSE: To prevent a hydraulic hose from being twisted or oil leakage from a connected part by communicating a swing frame side hydraulic pipeline and an in-bracket oil passage independently by way of a vertical axle oil groove and an in-vertical-axle oil passage.

CONSTITUTION: A boom bracket 7 is pivoted turnably on both ways by way of a vertical axle 70 which runs through the front end of a swing frame 4 vertically. The base end of a boom is pivoted turnably vertically by way of a boom support horizontal axle 71 which runs through the top of the bracket 7. The lower end of a boom operation hydraulic cylinder is pivoted turnably by way of a cylinder support axle 72 which runs through the front lower part of the bracket 7. Furthermore, a plurality of frame side hydraulic pipelines 14 and in-boom bracket oil passages 75 are communicated independently by way of vertical axle oil grooves 73 on the outer periphery of the axle 70 and in-vertical axis oil grooves 74 inside the axle 70.