This invention relates an image printing apparatus capable of copying by executing enlargement/reduction (E/R) processing optimum to an instructed mode. According to the apparatus, a copy mode and an enlargement rate are input. The use priority order of each enlargement/reduction (E/R) unit of the apparatus is decided. The enlargement rate is distributed to each E/R unit in accordance with the copy mode, decided use priority order, and the E/R rate upper limit value of each E/R unit. An image is copied by causing each E/R unit to sequentially execute E/R processing in accordance with the distributed enlargement rate and the decided use priority order and causing a printing unit to print based on the image data that has undergone the E/R processing.