Disclosed are a method and program for controlling communication of the target apparatus, specifically, blocking the communication of the target apparatus immediately and certainly in case where illegal connection to the target apparatus is detected in the network arranged one or more Layer-2 switches. The network monitoring manager H carries out blocking communication of the target apparatus immediately and certainly by detecting automatically the Layer-2 switch port connected to the communication apparatus, that is identified as the target apparatus including illegal connection, based on the MvP table, and blocking the communication of the target apparatus by administratively disabling the Layer-2 switch port connected to the target apparatus, in case where the network monitoring manager H detects illegal connection to the communication apparatus in the network.