This invention is directed to enhancement of flexibility when connecting an add-in card conforming to the PCI-Express specification. More specifically, the operation mode of the system board of a printing apparatus is configured to cope with both a root-complex and end-point. When an add-in card is inserted into an extension slot, the type of add-in card is discriminated by confirming the ON state of a detection pin. When the inserted add-in card operates as a root-complex, the system board is set to operate as an end-point. When the inserted add-in card operates as an end-point, the system board is set to operate as a root-complex.