There is provided an electronic apparatus which also enables the data input/output apparatus to be executed at a high speed to a small electronic apparatus having a limited installation space by using an IC card interface. In an electronic apparatus in which a detachable IC card is connected to an IC card junction portion and a CPU bus of the electronic apparatus main body is connected to the IC card by the junction portion and the IC card is used as an external memory device, there is provided pseudo card means having a junction portion which can be connected to the IC card junction portion of the electronic apparatus main body, and further, the pseudo card means has control means for converting the data input/output interface between the electronic apparatus and the pseudo card means and the data input/output interface between a predetermined external apparatus and the pseudo card means, wherein the data input/output operation can be executed between the apparatus main body and the external device at a high speed by using the bus of the IC card through the pseudo card means connected to the IC card junction portion.