An object of the invention is to provide a communication apparatus capable of communicating by transmitting and receiving a protocol signal in accordance with a predetermined protocol, when receiving a DIS without receiving an ANSam signal, or not receiving a CM signal within a predetermined period after transmission of the ANSam signal. With a line connection established, when a calling station receives a DIS without receiving the ANSam signal, the calling station sends a DCS signal or an NSS and then executes the protocol according to Recommendation T.30. Further, with a line connection established, when a called station does not receive the CM signal within a predetermined time t1 after transmission of the ANSam signal, the called station sends the DIS with bit number 6 reset, and executes the protocol according to Recommendations T.30 in response to the DCS signal or NSS sent from the destination communication apparatus. Furthermore, the protocol according to Recommendations V.8 and V.34 are executed in response to the CM signal or a CI signal in placed of the DCS signal or the NSS.