A processor according to an exemplary of the invention includes a first initialization unit which reads a first program for checking a reliability of the processor into a cache memory and executes the first program when the processor is started up, and a second initialization unit which reads a second program for checking a reliability of the cache memory into a predetermined memory area and executes the second program when the second initialization unit receives a notification indicating the completion of the establishment of a communication path between the predetermined memory area and the processor from another processor which exists in a partition in which the processor is added.