The present invention provides a unidirectional microphone by adding an output from an omnidirectional condenser microphone unit and an output from a bi-directional ribbon microphone unit together. A condenser microphone unit 10 and a ribbon microphone unit 20 are connected in series via a step-up transformer 30, and the respective sound signals from the microphone units 10 and 20 are added together and are output from a source S of an FET 14.