To realize a system capable of sharing a virtual device between multiple hosts.

Identifiers of the hosts 1 and 2 are registered in a source management list 32 in order of input request in relation to compound block identifiers of the virtual device 41. When the host 1 requests a compound block, whether the identifier of the host 1 is registered in relation to the compound block identifier or not is checked. In the case where it is not registered, the identifier of the host 1 is newly registered and notice that the compound block is secured is informed. In the case where it is already registered, each of the hosts registered in relation to the compound block identifiers reads the compound block from the virtual device 41 in order of request, and when one host concludes reading, notice that the compound block is secured is informed to a following registered host, and the host can reads the compound block on the basis of the notice, and as a result, exclusive control can be performed.