To detect defective rotation caused by the release of a wire and the abrasion of a bearing by providing a sensor arranged to detect a detected section adjacently to a pulley and a controller comparing the revolving speed of the pulley detected by the sensor with a set value.

When a wire 1 is normally and correctly set, the wire 1 is traveled in a groove between guide side wall sections 3 on both sides of a pulley. The pulley is rotated, a metal thin film 2 provided in the recess 6 of the guide side wall section 3 of the pulley is sensed by a proximity sensor 4 at every rotation, and an electric signal is outputted and sent to a controller. A counter provided in the controller counts the electric signals, the controller calculates the linear velocity of the wire 1 based on the count value within the prescribed time, i.e., revolving speed, and the diameter of the groove and compares the linear velocity value obtained from the calculation result with a set value set in advance. If the linear velocity value is within the range of the set value, the controller judges the rotation as normal and continues the operation.