To provide a miniaturized extending device that can certainly prevent the attachment and detachment of an IC card in a mounted state to the computer and improves the receiving sensitivity and portability of a communication device.

This extending device to be connected to an external port 2 of a computer 1 comprises an attaching/detaching section 31 for attaching/detaching a PIM (Personal Identity Module) card 3, a connector 11 connected to the external port 2 of the computer 1, a slider 13 that is disposed in parallel to the connector 11 and can move in the inserting/removing direction of the connector 11, and an energizing means (torsion spring 14) for energizing the slider 13 so that it projects in the tip direction of the connector 11. When the connector 11 is inserted into the computer 1, the slider 13 prevents the attaching/detaching of the PIM card 3 by covering the attaching/detaching section 31 of the PIM card 3 by inserting force.