PURPOSE: To enable plural keyboards to be connected to one device by performing a conversion processing by switching a processing to a developmental code conversion processing corresponding to the keyboard at the device side.

CONSTITUTION: Developmental code information with keyboard specification information generated by depressing the keyboard 001 is sent to a keyboard connection part 010 via a cable 004. On the developmental code information, the developmental code conversion processing corresponding to the keyboard 001 is applied at a key input data processing part 011. Similarly for the keyboard 002, the developmental code conversion processing corresponding to the keyboard 002 is applied when the developmental code information is sent. In such a way, it is possible to connect two or more keyboards to one keyboard connection part 010 in the device 003 in multidrop system.