In a virtual computer system controlling a disk volume and a virtual server which is connected to the disk volume, to which the area of the disk volume is allocated as a virtual disk and which executes a process using the allocated virtual disk, the virtual computer system erases information stored in the virtual disk allocated to the virtual server to be deleted correspondingly with the deletion of the virtual server. An administrative server may be provided to select a server system which is low in load from among plural server systems controlling virtual servers as a server system for erasing information stored in the virtual disk allocated to the virtual server to be deleted.