A method for accessing shared memory cards from each of plural processor cards is disclosed. The shared memory cards are composed of a shared memory card of an operating system and a shared memory card of a standby system in a redundant configuration, and each of plural processor cards individually access the shared memory cards. Each of the plural processor cards is connected to the shared memory card of the operating system and the shared memory card of the standby system in a point-to-point structure via corresponding serial buses and executes data transmission on a one to one basis to/from the shared memory card of the operating system and the shared memory card of the standby system.