A method of controlling a printing job of an image forming apparatus having an image forming unit. The method of controlling a printing job includes transforming scanned data into printable data, and determining a time to start driving the image forming unit according to the type of data scanned, starting driving the image forming unit at the determined start time, and printing the scanned data transformed into printable data. The time required to perform a printing job is thereby reduced, and scanned data can be output normally.