A maskless exposure apparatus which precisely and rapidly measures positions of spot beams of a plurality of optical systems by calculating positions of respective BMSs using a plurality of FMs engraved on an FBA on a movable table. The centers of the respective BMSs are aligned with the centers of random FMs of the plurality of FMs. Thereafter, positions of spot beams irradiated from the plurality of optical systems are quickly and precisely measured using the positions of the respective BMSs and the positions of the FMs measured by the BMSs, thereby more quickly generating mask data to execute maskless exposures.