PURPOSE: To apparently correct time lag by correcting the time lag produced by intermeshing gears through the use of a high speed at the time of changing over a pulse motor from backward running to forward running.

CONSTITUTION: At the time of changing a pulse motor from backward running to forward running in operating and driving an astronomical telescope to lead the star in search in its ocular, a time lag is produced because of the backlash between intermeshing gears g1, g2. In this invention, the speed of the forward running is made faster to be adapted to the correction of the time lag at the time of changing over from the backward running to the forward running and is changed to the diurnal motion speed after the correction. Such operation is accomplished automatically to apparently correct the time lag owing to the intermeshing of gears.