PURPOSE: To simplify and inexpensively manufacture the construction of a reversing device by coupling a resistance cam shaft and a reverse cam shaft through a ratchet mechanism only when the cam shaft is reversed, thereby eliminating a drive mechanism exclusive for a reverse rotation cam.

CONSTITUTION: One end of a ratchet 11 is coupled with a resistance cam shaft, and a ratchet pawl 12 is rotatably mounted on the arm rotary end of the ratchet 11 in the state always obliquely downward pressed by a fingerlike spring member 13. The rotational shaft of a ratchet wheel 15 is coupled with a reversing cam shaft. The resistance cam shaft and the reversing cam shaft are coupled through the ratchet 11 only when the cam shaft is reversed, thereby enabling to reverse the forward and backward movements of the cam shaft.