There is provided a tension adjusting mechanism which can prevent a dancer arm from being widely rotated and a peripheral roller such as a guide roller from early abrading even in the case a wire is tensioned or loosened in accordance with a speed increase or decrease of the wire. A plurality of dancer rollers are rotatably supported to a front end of a rotatable dancer arm. A plurality of guide rollers are disposed in such a manner as to oppose to the dancer rollers, thereby successively guiding one wire on the dancer roller through the guide rollers. A predetermined tension is applied to the wire by rotating and urging the dancer arm to one direction by an urging member.