Provided is a simple-structured tensioner that can ensure a smooth flow of oil while enabling a reduction in the production cost. A tensioner 10 includes a plunger 30 provided with a plunger through hole 32 extending from an outer circumferential surface to an inner circumferential surface of the plunger 30, and a tensioner body 20 provided with an oil supply hole 25 extending from an outer wall of the tensioner body 20 to the plunger bore 21. The oil supply hole 25 is formed in an elongated shape that extends along a protruding direction of the plunger.