To pass to a normal terminal with no delay for an inputted frame and to respond the terminal disable state to an upper device on the other hand by forming the terminal connection disable state into a prescribed response frame and sending it out to an outgoing call side.

A line branching device 2 branches one parent 1 which is connected from an upper primary station into branch lines 41 to 4N which are separately connected to N lower secondary stations, and has 'N+1' multipoint circuits 10 to 1N and N signal monitor circuits 21 to 2N. The result where a line state of each branching line 41 to 4N is monitored by the circuits 21 to 2N is stored in a terminal state table 32. When a communication control part 33 indexes the table 32 based on an address which becomes a destination identifier, i.e., a destination address of receiving frame which is inputted and judges that the table 32 is in an incoming call disable state, a negative response frame for an incoming call is sent out to an outgoing call side by the part 33 instead of an incoming call disable terminal.