Tensioner

A tensioner comprising:

• a plunger having a plunger hole that is open on a rear side;
• a housing having a plunger bore that is open on a front side and accommodates the plunger slidably;
• a main biasing means accommodated in an oil pressure chamber formed between the plunger and the plunger bore such as to freely extend and contract and urging the plunger to the front side;
• and a relief mechanism that relieves oil inside the oil pressure chamber out of the plunger when the oil pressure in the oil pressure chamber rises,
• the relief mechanism including a partition part that partitions inside of the plunger hole into the oil pressure chamber and an adjustment space and includes an internal relief hole that allows the oil pressure chamber to communicate with the adjustment space, an external relief hole formed to the plunger and allowing the adjustment space to communicate with an outer space, a piston set such as to be slidable back and forth with at least part thereof being positioned inside the internal relief hole, a piston biasing means that biases the piston toward the oil pressure chamber, and a piston restricting member set such as to be biased toward the front side by the piston biasing means and restricting movement of the piston toward the adjustment space,
• the piston restricting member having an orifice function that allows for control of an amount of oil discharged from the adjustment space via the external relief hole,
• wherein the piston biasing means comprises a coil spring,
• the piston restricting member having a shaft part extending continuously from a surface facing the adjustment space rearward, the shaft part being positioned radially inside the coil spring.