PURPOSE: To perform processing of the ordinary number of works by a second processing mechanism even when a deficiency in or an excess of the number of works processed by a first processing mechanism exists, in a synchronous drive device to perform synchronous operation of the first and second processing mechanisms.

CONSTITUTION: The output of a motor M1 arranged to a first processing mechanism is decelerated by reduction gears 21 and 22 and inputted to an encoder 45 through a frequency converting means 30. An electric signal from the encoder 45 is detected by a decoder 46 and based on the detecting output, the motor M2 of a second processing mechanism is controlled. When a deficiency in or an excess of the number of processed works occurs to the first processing mechanism, a phase converting means 30 is operated by means of a detecting means S. The phase of an electric signal inputted to the decoder 46 is delayed or advanced and this operation causes execution of synchronous correction of the deficiency in and the excess of the work between the first and second processing mechanisms.