Tensioner

A tensioner comprising;

• a power spring urging so as to resist a tension member receiving a load from a wrap-around transmission body;
• and
• a backup member being in contact with the power spring and supporting the power spring by acting an urging force in a direction opposite to a radial shift of the power spring in a direction in which the power spring is wound,
• wherein the power spring is unwound in a condition in which an inter-plate frictional force of the power spring is small in a case where an urging force acting from the power spring to the tension member is greater than a load acting from the tensioner member to the power spring and the power spring is wound in a condition in which the inter-plate frictional force of the power spring is large in a case where the urging force acting from the power spring to the tension member is smaller than the load acting from the tension member to the power spring.