A printing apparatus is equipped with multiple interfaces adapted to connect external devices adapted to store image data and operated by power supplied from a first-connected external device, and is adapted to print images stored in the external devices. The state of the connection of the external devices to the plurality of interfaces is detected and, when it is determined that a plurality of external devices are connected to the printing apparatus, a determination is made as to whether or not an amount of power required by the plurality of external devices exceeds the amount of power the printing apparatus is capable of supplying. If the amount of power requested exceeds capacity, then the apparatus selects which external device to supply with power depending on the operating state of the first-connected external device.