Disclosed herein are a maskless exposure apparatus configured to perform exposure by tilting a beam spot array with respect to a scan direction (Y-axis direction) thus preventing stitching stripes and a stitching method using the same. A step distance, in which exposure dose uniformity in a stitching area is within a tolerance range, is calculated using actual position data of beam spots constituting the beam spot array on an exposure plane, and if necessary, using beam power data and/or beam size data. As exposure is performed based on image data conforming to the step distance, the stitching area has a uniform exposure dose, enabling exposure without stitching stripes.