A microphone adapter is attachable to a microphone including a microphone unit and a casing having a front sound terminal and a back sound terminal. The microphone adapter has a bottom having a hole through which the casing of the microphone extends and a cylindrical peripheral wall integrated with the bottom, having an open end opposite to the bottom, and covering the periphery of the back sound terminal. The cylindrical peripheral wall has an internal diameter larger than the external diameter of the casing of the microphone so as to define a space between the cylindrical peripheral wall and the external peripheral surface of the casing of the microphone extending through the hole, and extends from the bottom at least to a position of the front sound terminal in a sound collection axis direction.