The present invention enables to update a program in a storage control device while processing access requests, without imposing any burden on a host. When execution of updating of a program is commanded from a management terminal, an update control unit starts within the controller which is the object of updating. After a host I/F unit has been connected to an access request processing unit within another controller by a connection control unit, the update control unit updates a program which is stored in a program memory or a boot disk. When this updating is completed, the update control unit reconnects the host I/F unit to its access processing unit by the connection control unit. Since the stored contents of data memories are synchronized, the other access request processing unit can continue processing access requests from the host in place one access request processing unit.