A tensioner capable of keeping oil pressure in an oil pressure chamber stable is provided. In the tensioner, a flow amount control mechanism includes a flow amount control member set inside a control space so as to be able to approach and separate from the oil pressure chamber, a control biasing unit, a first restricting part and a second restricting part. The flow amount control member and the inner wall of the control space are provided such that the flow resistance of a first control flow passage, which is exhibited when the flow amount control member contacts the first restricting part, is larger than the flow resistance of a second control flow passage, which is exhibited when the flow amount control member contacts the second restricting part.