PURPOSE: To easily switch an operation to the one to load another ROM when part of information in a ROM is changed by controlling a readout means so as to read out the information from either first or second ROM having a common address storage area.

CONSTITUTION: The equipment is formed in such a way that the ROM1 mounted on a printed board, the ROM2 loadable at need, and a jumper plug JP can be loaded and switched manually by removing a main body back plane cover 201. The plug JP operates the ROM1 by connecting terminals 1 and 2, however, when the bug exists in the ROM1, the ROM2 is loaded, and the terminals 2 and 3 of the plug JP are connected, and the terminals 1 and 2 are disconnected. The content of the ROM2 conforms to the leading areas 0000-FFFF of the area of the ROM1, and the same address is attached. Therefore, the decoded output l1 of the address is connected to l2, and is inputted to the chip seect CS2 of the ROM2. And the content is outputted to a data bus DB with a readout signal RD, and hereafter, the operation is performed with the ROM2.