In a data center architecture or the like, the present invention provides a method for setting up hosting environments concurrently by loading a boot image by means of network boot or the like, allowing for fast booting even with a large boot image, while preserving security. A boot image is divided into a plurality of parts. Computer resources have their public keys stored in their BIOS ROMs and e-signatures are attached to the boot image parts with a private key corresponding to one of the public keys. Also, priority levels in e-signature verification are assigned to the boot image parts. A boot instruction includes priority level setting. Only for boot image parts with that priority level or higher, e-signature verification is performed. By this manner, booting can be performed faster than booting involving verification of the e-signature to a whole boot image.