Maskless lithographic apparatus measuring accumulated amount of light is provided. The maskless lithographic apparatus includes a light source which emits light, a stage on which a substrate is disposed, an optical system which converts the light into a beam spot array including a plurality of columns and a plurality of rows and irradiates the beam spot array onto the stage, a slit to which the beam spot array is irradiated and which passes an nth (n is a natural number) row of the beam spot array, an optical sensor which senses the nth row of the beam spot array which has passed through the slit, and a measuring unit which measures an accumulated amount of light in the nth row of the beam spot array sensed by the optical sensor.