BOOM STRUCTURE

PROBLEM TO BE SOLVED: To prevent a piping hose from rubbing while retaining the strength of the boss by fitting a boom body swinging around the boss to a boss base plate so as to cover the boss base plate having a face spread to the radial outside. SOLUTION: A bottom plate 59 is welded to the lower end of an upper plate 58 so as to cover the opening bottom of the upper plate 58 having an inverted U-shaped section to form the boom body 54 of a second boom 29. An inverted U-shaped holding member 66 is provided at the top face 60 of the upper plate 58 of the boom body 54, and a pipe 68 to feed hydraulic oil to a bucket cylinder or an arm cylinder or the like is inserted in the holding member 66 and retained therein. The boss 56 is fixed in an inserted manner to both longitudinal ends of the bottom plate 59 of the boom body 54, and a boss base plate 64 having a face spread to the radial outside of the boss 56 is fitted to the radial outside end of the boss 56. Further, the second boom 29 is connected to the first boom swingably supported on the revolving body of a back hoe so as to be freely swingable around the boss 56. In this way, the pipe 68 can be prevented from rubbing while securing the strength of the boss 56.