Multistage telescopic arm device and deep digging machine equipped with multistage telescopic arm device

摘要

An expandable actuating sheave mounted on a sheave mounting unit is prevented from being largely protruded from an outer surface of an outer shell wherein an expanding cylinder is installed. The sheave mounting unit (29) consists of a pair of left and right connection beams (30) disposed on both sides of the left and right with the expanding cylinder (25) therebetween; an expandable sheave supporting axis (30B) and a pushing-in sheave supporting axis (30C) provided on each of the connection beams (30); and an upper connection arm (31) and a lower connection arm (32) which makes a connection between the left and right connection beams (30) beyond the expanding cylinder (25). Thus, the expandable actuating sheave (40) supported on the sheave mounting unit (29) can be disposed on the far outside from a left side surface (13C) of the outer shell (13). Consequently, while ensuring a large diameter of the expandable actuating sheave (40), the expandable actuating sheave (40) can be prevented from being largely protruded from a back surface (13A) of the outer shell (13), thereby providing the expandable actuating sheave (40) having a large diameter.