1. A detection method of omission-in-software-property-management using a network for detecting a computer omitted from a software-property management which manages, for each computer, basic information thereof and installed software, and fix-patch application status, the method comprising the steps of: performing a first step wherein a network-connected-computer list which holds, for all computers connected to a given network, information for identifying each computer, and a software-property management list which holds, for all computers to be managed by said software-property management, information for identifying each computer, are used as a basis on which a computer is extracted that is present in said network-connected-computer list and absent in said software-property management list; and performing a second step wherein there is created a list of computer omitted in the software-property management based on the computer extracted that is present in said network-connected-computer list and absent in said software-property management list in the first step, wherein in the first step, said network-connected-computer list and said software-property management list are used as a basis on which a computer is extracted that is present in said software-property management list and absent in said network-connected-computer list, and in the second step, there is created a list of computer in unused state based on the computer extracted that is present in said software-property management list and absent in said network-connected-computer list.