Tensioner

A tensioner comprising:

• a movable section configured to receive a load from an entrained transmission body through a tension member;
• a fixed section configured to support the movable section so as to be capable of being displaced;
• a flat spiral spring biasing the movable section so as to resist the tension member, the flat spiral spring unwinding in a state in which there is a small inter-plate friction force in a case in which there is a large biasing force applied to the tension member to counter the load acting from the tension member, and winding-up in a state in which there is a large inter-plate friction force in a case in which there is a small biasing force applied to the tension member to counter the load acting from the tension member;
• and
• a wind-up limiting section configured to limit wind-up of the flat spiral spring,
• wherein the wind-up limiting section includes a resistance force imparting section that is disposed inside an inner circumferential face of the flat spiral spring and configured to apply a biasing force against a decreased diameter of the flat spiral spring.