To provide the length measurement device of a wire type wherein a reel diameter and a wire diameter are not needed to be controlled, and capable of performing highly precise measurement and suitable for miniaturizing.

The main pulley 4 is provided freely and rotatably in the casing 2, and the wire 24 is wound on the main pulley 4. The wire 24 is wound on the length measurement pulley 14, and is guided to the direction of outgoing port of the casing 2. The main pulley 4 is energized to the wire winding direction by a winding energizing means. The input shaft of the encoder 8 coordinating with the supporting shaft of the length measurement pulley 14 converts the rotation of the length measurement pulley 14 into an electronic signals. The wire 24 is constituted with a flat belt-like toothed wire, and on the circumferential face for guiding the wire of the length measurement pulley 14 recessed grooves 34 for engaging with the teeth of the wire 24 are formed.