1. A management apparatus comprising: a communication interface device which is coupled to the communication network; a storage resource which stores attribute/protocol management information denoting multiple attribute/protocol relationships; a processor which is coupled to the communication interface device and the storage resource, wherein the storage resource stores attribute/protocol management information denoting multiple attribute/protocol relationships, the attribute/protocol relationship is a corresponding relationship between a communication apparatus attribute and a management protocol, which is inferred to be the optimum for the communication apparatus having this communication apparatus attribute, the attribute/protocol management information comprises port definition information, each attribute/protocol relationship of the port definition information is the corresponding relationship among port identification information, a management protocol referred to be the optimum for a communication apparatus for which this port is open, and the probability that this management protocol is the optimum for the communication apparatus for which this port is open, and wherein the processor is configured to carry out the following processing for each of multiple addresses to detect an unknown communication apparatus which might exist in the multiple addresses in the communication network but is not detected by the management apparatus: (A) sending a query specifying an address from the management apparatus and checking that the management apparatus receives a response to this query; (B) writing, in a case where the response to this query has been received from the unknown communication apparatus, which is at the address specified in this query, to the storage, resource query result information, which denotes the corresponding relationship between the address specified in this query and the communication apparatus attribute acquired based on this response; (C) identifying from the attribute/protocol management information a management protocol that corresponds to the unknown communication apparatus attribute denoted by the query result information; and (D) deciding, based on the identified management protocol, the optimum management protocol for this address, and treating the unknown communication apparatus as detected, and wherein in a case where a connection cannot be made using a first management protocol with respect to the address: in the (A), the processor is configured to issue an open port identification information query with respect to the address; in the (B), based on this response, the identification information of one or more open ports from among one or more ports used by the communication apparatus, which is the source of this response, is acquired, and, in addition, the query result information is information denoting the corresponding relationship between the identification information of these one or more open ports and the address; in the (C), the processor is configured to identify from the port definition information one or more management protocols and probabilities corresponding to the identification information of one or more open ports denoted by the query result information; and in the (D), the decided optimum management protocol is the management protocol that has been decided on based on the one or more management protocols and probabilities.