PURPOSE: To suppress the variation of the torque and to prevent electronic parts from coming off or shifting, by constituting an index rotation driver for a rotary head out of the first index rotating means and second index rotating means having a counter torque characteristic.

CONSTITUTION: The thread of a roller gear cam 6a is formed in the direction opposite to that of a roller gear cam 5a, and the first index rotating means 5 and second index rotating means 6 have torque characteristics opposite to each other. And a rotary head 1 is driven by the first index rotating means 5 and index-rotates. On this occasion, the torque of the first index rotating means 5 varies, but this variation is canceled by the second index rotating means 6 having a counter torque characteristic. Accordingly, the torque is leveled when the rotary head 1 is rotated. This suppresses the variation of the index rotational speed of the rotary head 1, and it becomes possible to prevent electronic parts held by air-suction transferring and mounting head 2 from coming off or shifting.