The communication signal generating device is for use in a communication system where communication signals each of which is set at a first level or a second level are exchanged among a plurality of communication apparatuses through a communication line. The communication signal generating device includes a switching element provided in a communication line to connect the communication line to a ground or a constant voltage source, and a driving means to generate a first communication signal at the first level by turning on the switching element to thereby pass a certain current to the communication line, and generate a second communication signal at the second level by turning off the switching element to thereby pass no current to the communication line. The driving means is configured to gradually increase an output impedance of the switching element during one bit time of the first communication signal.