A carbon granule microphone with carbonaceous electrodes, which is lower in cost and more convenient for mass production than the conventional microphone with gold plated electrodes, was studied as a telephone microphone. A molded piece made from a mixture of synthetic resin and carbon powder can be used for the back electrode and paint made from it can be used to coat the dome electrode. A new microphone, whose sensitivity is as high as a conventional microphone, shows higher resistance. This means that the efficiency of the new microphone seems to be slightly less. However, the sensitivity change in the new microphone under excitation by voice is less than that of the conventional microphone. The new microphone sensitivity dependence on DC input power is almost the same as that of a conventional microphone.