To reduce a load of a tensioner lifter, enhancing the oscillation absorption function of the tensioner lifter in a chain tensioner. In a chain tensioner provided with a tensioner arm 16 rockably supported by fixed structure Ea and relatively slidably touched to the outside on the loose side of a transmission chain 14 without an end coupling a driving sprocket 11 and a driven sprocket 12 and a tensioner lifter 18 supported by the fixed structure Ea for pressing the tensioner arm 16 on the side of the transmission chain 14, a control arm 17 rockably supported by the fixed structure Ea for transmitting the pressure of the tensioner lifter 18 to the tensioner arm 16 is inserted between the tensioner arm 16 and the tensioner lifter 28.
