EXCAVATOR

PURPOSE:To prevent interference of a bucket with booms and an arm cylinder by performing a change of an angle of refraction between booms with a telescopic cylinder, and arranging the telescopic cylinder in the center side of the turning of the booms. CONSTITUTION:In the case that an angle alpha of refraction between booms is small, when a telescopic cylinder 1 arranged in the back surface of a lower boom 2 is operated for extension, an upper boom 5 is turned around of lower supporting part 21. Next, a supporting part 22 of the lower end of a joint link 6 is turned around of the lower supporting point 21, and the joint link 6 is pulled backward around of the supporting part 22. Next, an arm cylinder supporting part 17 of an arm cylinder 4 is moved backward, and an angle betaof refraction of an arm is enlarged. In the case that the angle alpha of refraction between booms is large, when the telescopic cylinder 1 is operated for reduction, the supporting part 22 is raised. Furthermore, the joint link 6 is turned forward to reduce the angle beta of refraction of the arm.