A focusing device for use in micro film readers or the like for projecting micro images to give in-focus conditon exactly and readily. The present device includes a memory for storing a distance data representing the distance between an original and a projective lens at in-focus position thereof, and a sensor for measuring the distance between an original and the projective lens wherein the projective lens is moved to the in-focus position by a focusing motor in response to the distance data stored in the memory and a signal representing the measured distance generated from the sensor.