When initializing a card-shaped device inserted in a card interface, operation mode acquiring means incorporated in an electronic device acquires operation mode information, stored in a register file incorporated in the card-shaped device, by a predetermined procedure using a predetermined pin. Operation mode setting means incorporated in the electronic device executes signal assignment on a plurality of data pins peculiar to an operation mode indicated by the acquired operation mode information, thereby switching a data transfer width, and allowing the card-shaped device to operate in the operation mode.