An object of the present invention is to provide a tensioner that has a reduced number of components and lighter weight and is easy to assemble. The tensioner according to the present invention is configured such that a base member is detachably and mechanically joined to a rear end opening of a cylindrical plunger with a closed front end against the resilience of biasing means that is accommodated inside the plunger such as to be freely extend and contract. The joint between the plunger and the base member is a mechanical connection that is one of a thread engagement, a press-fit, and a pin connection.