PURPOSE: To improve the swingability and improve the stability of a hydraulic digger by furnishing at the boom side halfway point of the outside of a base end arm a two-step type drive drum that is driven by means of a hydraulic motor and is for a pulling-in rope and a pressing rope. ;CONSTITUTION: A two-step type drive drum 81 in which a pulling-in rope drum 81A and a pressing rope drum 81B having the 1/2 diameter of its diameter are integrally made, is furnished to the halfway point of the boom 2 side of the outside of a base end arm 11a. Next, one end of the pulling-in rope 83 is fixed at the pulling-in rope drum 81A and hung-wound, and connected to the base end portion of a tip arm 11n via the idly moving sheave 84 of the base end portion of the base end arm 11a. Also, one end of the pressing rope 85 is fixed at the pressing drum 81B and hung-wound, and connected to the base end of a middle arm 11b via the idly moving sheave 86 of the tip portion of the base end arm 11a. As a result, a distance to the drive drum 81 from the tip of the boom 2 becomes small, and as an inertia moment is small, swing work can be easily conducted.;COPYRIGHT: (C)1996,JPO
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