A unidirectional dynamic microphone includes a grip housing, a microphone unit supported at a first end of the grip housing, a plug assembly attached to a second end of the grip housing and connected to the microphone unit through a lead line, and an air room serving as a part of an acoustic circuit of the microphone unit in the grip housing. The grip housing has a fitting part for the plug assembly and an expanded portion. The plug assembly fitted in the fitting part is fixed within the grip housing by an elastic ring and a pressure ring fitted in the expanded portion. The elastic ring seals a space between the grip housing and the plug assembly.