A connection monitoring device includes: first and second connection systems in which monitored devices are connected in cascade in forward and backward directions, respectively; a storage unit to store configuration information on connection configuration of the monitored devices and connection permitting information including information on a path permitted between the connection monitoring device and the monitored devices within paths undefined in the configuration information; and a control unit to change from a first monitoring state in which the connection configuration of the monitored devices is monitored in accordance with the configuration information to a second monitoring state in which the connection configuration of the monitored devices is monitored in accordance with the configuration information and the connection permitting information in a case where a configuration modification, accompanied with cutting of any one of connections of the first and second connection systems, of the monitored devices is performed.