This invention is directed to reducing power consumption even when there is a great amount of power consumed by a root complex in a printing apparatus that employs a PCI Express architecture. To accomplish this, a printing apparatus that includes a controller capable of switching between a root complex and an endpoint and an accelerator controller serving as a root complex performs the following processing. More specifically, in the power saving mode, the power source of the accelerator controller is turned off and the controller is set as a root complex. Power consumption in the power saving mode can be greatly reduced, and a return sequence from the power saving mode can be executed.