To provide superior attenuation characteristics by arranging a plurality of laminated disc springs which energizes a first end part in the direction for projecting a piston inserted in a hole of a housing therefrom in a second end part, and providing a tensioner arm in the first end part.

A tensioner 10 is provided with a housing 11 having a hole 12 formed therein and a piston 20 energized by a disc spring assembly 30 constituted of some disc springs which are connected in series and whose adjoining two disc springs are not arranged parallel. The tensioner 10 incorporates a tensioner arm 25 being in contact with a chain 15. When the chain 15 is loosened, the disc spring assembly 30 pushes the piston 20 so as to tension the chain 25. The piston 20 pushes the chain against the increase in its tension force till the presser force from the chain 15 exceeds the spring force and when the tension force exceeds it, the piston 20 is retreated into the hole 12 and holds the position of the piston 12. This constitution can eliminate any possibility of the chain 15 from exceeding the fatigue limit.