Telescopic boom assembly

Telescopic boom assembly (15c) with at least two boom parts (20, 21), comprising an outer boom part (20) and an inner boom part (21) which is movable in the longitudinal direction inside the outer boom part (20). A channel (30) is defined between the outer wall structure (21 c) of the inner boom part and the inner wall structure (20c) of the outer boom part, extending in the longitudinal direction inside the boom assembly (15c). A flexible energy transmission chain (24) is placed in the channel (30), inside which chain hoses, cables or the like are placed and which can be folded up and folded out when the inner boom part (21) moves inside the outer boom part (20). Furthermore, the boom assembly comprises at least one support (22) moving with the inner end (21 a) of the inner boom part and supporting the inner end (21 a) of the inner boom part to the inner wall structure (20c). The telescopic boom assembly (15c) can be placed in an articulated hoist boom or in a movable working machine, particularly a forest machine.