Provided is a tensioner capable of reducing a machining or mounting load and preventing leakage of oil from a surface for mounting a tensioner with a simple configuration. A tension body having a plunger-receiving hole into which a plunger is slidably inserted is configured to have a projection portion on a mounting surface that face a wall surface having an oil discharge hole of amounting target object. The projection portion is configured to be inserted into the oil discharge hole and to be continuously connected to the oil supply path formed in the tensioner body to form an oil passage.