To provide a tensioner in which a bearing of the drive shaft of the conventional art is not necessary and also that enables the initial load of the torsion spring to be retained in an intact condition when the tensioner is disassembled for maintenance purposes or the like. The tensioner is designed such that it includes (1) two shaft members that compose a set and that are engaged by screw portions, and (2) a spring that is inserted in the driving unit by fastening onto the aforementioned two shaft members the hooking portions that are located at each end of said spring, and such that said spring is inserted in the set of the shaft members under an appropriate windup condition, and that one shaft member moves forward from the loaded strength by the aforementioned spring, (3) the aforementioned driving unit, (4) a case into which said driving unit is inserted, and (5) a system that prevents the aforementioned driving unit from coming off the case.