A device driver includes an access permitted directory storage unit and an access-permission determining unit. The access-permitted directory storage unit stores as an access-permitted directory an activation directory for a process that is allowed to access an S memory (private memory). The access-permission determining unit checks whether an activation directory for a process that has requested for access to the S memory matches the access-permitted directory. Based on the result, the access-permission determining unit determines whether to accept the access request.