To provide a simple design chain tensioner that enables formation with fewer components and simplifies assembling process, and is capable of driving a chain stably, thereby reducing wear or occurrence of breakage and improve durability. The chain tensioner 100 includes a chain-drive guide shoe 130 pivotally supported on an arm 120 provided to a tensioner body 110. A bushing part 140 of the chain-drive guide shoe 130 includes a mating hole 141 to mate with a first pin portion 122 that extends from the distal end of the arm 120 to one lateral side, and a guide part 142 guided by a part of a second pin portion 123 that extends to the other lateral side, and a slit 143 wider than a portion of the arm 120 facing the chain-drive guide shoe 130 is provided between the mating hole 141 and the guide part 142.