A telescopic device comprising: a pair of outer casings; insertion bodies telescopically inserted one in each of the outer casings; a plurality of vertically-arranged rung members each providing a connection between the paired outer casings; a locking mechanism mounted at each of the outer casings for securely holding the insertion body in a telescoped position relative to the outer casing; and operating means having an operating member for unlocking each of the locking mechanisms, the locking mechanism comprising a retention portion disposed at the insertion body and a locking member supported on the outer casing in movable relation toward and away from the retention portion for engagement with and disengagement from the retention portion, the locking member serving as a telescopic system interlocked to the operating member extending from the locking mechanism to a position near the upper rung member, the operating means comprising an operating rod for coupling the paired operating members for concurrent movements in an unlocking direction, each end of the operating rod and corresponding one of the paired operating members being fitted to each other in a manner such that, when manipulating one end of the operating rod in an unlocking direction, the operating rod is inclined with consequent movement of one of the operating members alone in the unlocking direction, characterized in that the operating means comprises an engagement portion disposed at an upper part of each of the operating members and a linkage portion disposed at each end of the operating rod in engageable relation to the engagement portion, and wherein, in between one of the linkage portions and the corresponding engagement portion, as well as in between the other one of the linkage portions and the corresponding engagement portion, there is left a play for movement of the linkage portion from a position out of engagement with the engagement portion to a position in engagement with the engagement portion. a pair of outer casings; insertion bodies telescopically inserted one in each of the outer casings; a plurality of vertically-arranged rung members each providing a connection between the paired outer casings; a locking mechanism mounted at each of the outer casings for securely holding the insertion body in a telescoped position relative to the outer casing; and operating means having an operating member for unlocking each of the locking mechanisms, the locking mechanism comprising a retention portion disposed at the insertion body and a locking member supported on the outer casing in movable relation toward and away from the retention portion for engagement with and disengagement from the retention portion, the locking member serving as a telescopic system interlocked to the operating member extending from the locking mechanism to a position near the upper rung member, the operating means comprising an operating rod for coupling the paired operating members for concurrent movements in an unlocking direction, each end of the operating rod and corresponding one of the paired operating members being fitted to each other in a manner such that, when manipulating one end of the operating rod in an unlocking direction, the operating rod is inclined with consequent movement of one of the operating members alone in the unlocking direction, characterized in that the operating means comprises an engagement portion disposed at an upper part of each of the operating members and a linkage portion disposed at each end of the operating rod in engageable relation to the engagement portion, and wherein, in between one of the linkage portions and the corresponding engagement portion, as well as in between the other one of the linkage portions and the corresponding engagement portion, there is left a play for movement of the linkage portion from a position out of engagement with the engagement portion to a position in engagement with the engagement portion.