PURPOSE: To enable a follower shaft to be prevented from being suddenly accelerated by installing a clutch which controls the transmission of power from an output shaft to said follower shaft so as to put another clutch in engagement when the rotating speed of said follower shaft is the same as that of said output shaft.

CONSTITUTION: In order to make a prime mover shaft 1 and a follower shaft 6 to engage with each other at a fixed position and to run continuously from the state in which said prime mover shaft 1 is continuously running while said follower shaft 6 is at a standstill, a clutch 5 which controls the power transmission of an output shaft 3 and said follower shaft 6 is activated and put in engagement just when said output shaft 3 comes to a standstill during its intermittent rotation or reciprocating rocking motion. Said output shaft 3 of a cam mechanism 7 then begins to rotate by being driven by a cam 71 fixed on an input shaft 2. Since a clutch 4 is activated and put in engagement, during the time in which said prime mover shaft 1, said follower shaft 6, and said output shaft 3 are running at the same speed, the sudden acceleration of said follower shaft 6 can be thus avoided.