To obtain an operating apparatus for locking the conductor clamp means of a spacer for overhead transmission lines which facilitates locking operation in an elevated position.

The frame of a lock-operating means is provided with a pair of receiving portions 39A and 39B, which receive the base of a fixed clamp arm 5 and the sides of the tip of the movable clamp arm 6 of conductor clamping means 4A-4D of a spacer 2 for overhead transmission lines, and a pressing means 40 which presses the end of the base of a locking member 9A of a locking means 9 at a position facing the area between the pair of the receiving portions 39A and 39B. Since the base of the fixed clamp arm 5 of the conductor clamping means 4A-4D and the sides of the tip of the movable clamp arm 6 are received by the pair of the receiving portions, and the end of the base of the locking member 9A is pressed by the pressing means 40 in the position facing opposite the area between the pair of the receiving portions, locking operation can be performed without rotating the conductor clamping means 4A-4D, and this has advantage in facilitating locking operation in the elevated position.