A chain tensioner device having a first slide surface of a main arm pivotably supported at an upper end thereof, and a second slide surface of a sub-arm pivotably supported at a lower end thereof. The first and second slide surfaces slidably abut against each other. When the main arm is biased toward a timing chain via the sub-arm by a biasing force of a plunger of a tensioner lifter, a stroke of the main arm is increased with respect to a stroke of the plunger.