Expander and wire stretching apparatus

The present invention provides an expander and a wire stretching apparatus enabling wire stretching work to be performed easily and accurately. According to an aspect of the present invention, an expander used for stretching a wire rod is provided. The expander comprises an outer cylinder, an inner cylinder, an actuating portion, a driving portion, and a position detecting portion. The inner cylinder is inserted into the outer cylinder from one end in an axial direction. The actuating portion has a screw axis inserted into the outer cylinder and the inner cylinder, and a nut fixed to other end of the inner cylinder in the axial direction and screwed to the screw axis. The driving portion is configured to allow the nut to move along the screw axis by allowing the screw axis to rotate around an axial center. The position detecting portion is provided on an outer peripheral side of the outer cylinder and has at least one sensor for detecting a position of the nut.