A computer on which OSs run is coupled to the storage apparatus, the OSs include a first OS controlling access to the storage apparatus and a second OS generating a virtual computer. A logically divided computer resources are allocated to the first OS and the second OS respectively. A third OS for executing an application runs on the virtual computer. The second OS has a shared region management part managing a shared region that is a memory region used for communication between the application and the first OS. The third operating system has an agent requesting the second operating system to secure the shared region based on a request from the application and mapping the secured shared region to a guest virtual address space.