Abstract: An apparatus and method for establishing construction information of an unmanaged Ethernet switch which is capable of readily replacing a memory according to a construction form of each option slot without opening or closing an outer casing. In the apparatus for establishing construction information of an unmanaged Ethernet switch, a first memory storing switch construction information, in the case where there is no option board mounted in an option slot, is positioned on a main board, and a second memory storing switch construction information, in the case where there is a option board in the option slot, is positioned on the option board, so that when there is no option board in the option slot, the first memory is automatically used, and when there is an option board in the option slot, the second memory is used.