<p>Log memories (log memories 6a-6b) for recording updated history of a main memory 7 are provided. CPUs 2a-2c record the updated history of the main memory to either of the log memories and writes context thereof and content of a cache memory to the main memory at a checkpoint acquisition. The updated history of the main memory is switched from one of CPUs that has finished a checkpoint processing to other one of the log memories in which the CPUs do not use to record the updated history of the main memory. Normal processing is restarted without waiting for finishing the checkpoint acquisition of the other ones of CPUs. <IMAGE></p>
