Abstract: A serial scanner apparatus, correction method thereof, and storage medium for performing bi-directional reading with high precision and greatly improving the reading speed. A carriage is first driven in the forward direction, then reversed, and driven in the backward direction. The carriage is accelerated until the speed reaches a predetermined velocity v1. When the predetermined velocity v1 is reached, the carriage is driven at constant speed. In the head portion of the constant-speed driving area, a correction area (reference correction area), having the same distance as that of the correction area for forward driving, is provided. With the use of an area (actual correction area) obtained by adding an area for correction time stored by a controller unit to the reference correction area, read-start timing is adjusted and the bi-directional error is corrected.