To accurately detect the wear of a guide roller with simple constitution and to appropriately detect the replacement timing of the guide roller.

A specified rotation angle range (a groove 70) of one rotation of a guide roller 16 is detected by a proximity switch 100, and pulse signals of a fixed cycle are outputted from a pulse generator 104. In a signal processing circuit 102, the pulse signals outputted from the pulse generator 104 are extracted while the groove 70 is detected by the proximity switch 100, and the pulse number is counted by a pulse counter 106. An arithmetic part 108 judges the rotating speed of the guide roller to be increased by wear in the case of the pulse number being smaller than the specified threshold value in relation to the travel speed of a wire, and the wear of the guide roller 16 is displayed by a display part.