PURPOSE: To display message data by utilizing a message display program integrated on the side of the main body of the equipment even while executing an external program at the message display device to display message data corresponding to the HELP key operation of the compact electronic equipment which can connect an external storage device.

CONSTITUTION: The leading address of a card side HELP processing program is previously set to a header area 17a of a ROM card 17 and in the case of the 'HELP' key operation, either the routine message of a main body ROM 13 or the arbitrary message of the ROM card 17 is selected by the card side program. The leading address of the message data is set to an address register 14c of a RAM 14, and the routine message or the arbitrary message is read corresponding to the leading address set to the address register 14c, and displayed on a display part 15 by the message display program on the main body side.