Provided is a simple-structured tensioner that can reduce processing and assembling workload as well as increase the degree of design freedom. A tensioner (10) includes an oil supply hole (33) formed in a sleeve bottom (32) and a check valve (50) disposed on a front face of the sleeve bottom (32). The check valve (50) includes a check ball (51) and a retainer (52). The sleeve bottom (32) includes a ball seat (34) which protrudes in a cylindrical shape toward the front side integrally with and continuously from the edge of the oil supply hole (33) and on which the check ball (51) is seated.