A main logical unit and a standby logical unit are defined by a process controller in a shared main memory multiprocessor, and an information storage space accessible from both logical units is provided. The main logical unit stores address information onto that information storage space by indicating a memory area it controls as the main memory area. When failover or cloning becomes necessary, the standby logical unit searches the information on the applicable address. Then from the applicable information, it also searches information on the main memory area controlled by the main logical unit to establish in itself and forms a processing environment and state identical to the main logical unit such that the standby logical unit takes over all or a portion of the processing of the main logical unit. This enables the construction of a server system of high operability to overcome failures and poor response times by failover and cloning, etc.