In a printing apparatus using a printhead having an array of printing elements in which a plurality of printing elements are arranged in a predetermined direction, the printing apparatus performing printing by scanning the printhead over a printing medium in a direction crossing to the predetermined direction on the basis of information transmitted from a host apparatus, print data transmitted from the host apparatus is stored in a buffer, printing by the scanning is started when the print data stored in the buffer reaches a first amount that is smaller than an amount of print data to be printed on the printing medium by the printhead by one scanning, the scanning is interrupted when storage of the print data in the buffer is delayed during the scanning, and when, after the interruption, subsequent print data stored in the buffer reaches a second amount, the interrupted scanning is executed to complete printing by one scanning. Accordingly, with an inexpensive arrangement having a memory whose capacity is smaller than the data amount to be printed by one main scanning, interruption of printing/scanning can be suppressed, and even when printing/scanning is interrupted halfway, high-quality printing can be performed.