A method for detecting the leading edge of a sheet of print medium by driving a line feed motor at a predetermined speed; scanning and storing a data block of the sheet by slices; determining the leading edge of the sheet, based on the scanned and stored data; calculating sheet position according to the edge determination, and calculating a drive value of the line feed motor according to the sheet position; and second driving the line feed motor according to the calculated drive value. The data of the scanned data block is stored such that a scanning level of pixel data for a given horizontal line is regularly stored in an address memory, and the determining step searches for a boundary on which both near-absolute black and near-absolute white pixel data values are indicated in the scanning and storing step.