The present invention discloses a technique of determining actual effect information actually related to cause information occurring in a multiplexer having the function of multiplexing communication lines, and the redundancy function. It is an object of the invention to determine the actual effect information at a high speed by providing an information input portion to take as inputs cause information and effect information collected in relation to components of a network having a multiple hierarchical configuration, a storage portion to contain hierarchical data for mutually correlating the components of the network having the multiple hierarchical configuration, and a processing portion to retrieve the hierarchical data from the storage portion depending upon the cause information input into the information input portion, thereby using the retrieved hierarchical data to extract the effect information input into the information input portion so as to determine the actual effect information actually related to the cause information.