To adjust an advanced amount of a push-rod minutely and to work a rack effectively in a ratchet automatic tensioner.

The ratchet automatic tensioner is provided with the push-rod 30 movably supported in a tension body 31 in the rod axis direction, a coil spring 33 energizing the push rod 30 to a cam chain, etc., and two pairs of ratchet mechanisms for preventing a reverse movement. A plurality of racks 50 and 51 having a tooth row of the same pitch P are formed at the same phase in the push-rod 30 in the rod axis direction, and ratchet claws 55 and 56 engaged with each rack 50 and 51 respectively are provided in the ratchet body 31 at the phase being shifted approximately half an pitch with each other.