Provided is a microphone, wherein changes in frequency characteristics resulting from diffraction/reflection are minimized. The present invention has: a casing having an opening at the top surface thereof; and an omnidirectional microphone unit built into the casing and provided within the opening. Of the top surface of the casing, the distance to the opening from an edge demarcated as the boundary between the bottom surface or lateral surface and the top surface across the entire perimeter of the top surface changes across at least half of the entire perimeter of the edge, and the average value of the distance from the edge to the opening is configured at a size that is shorter than half of the wavelength of sound of a frequency region at which human auditory sensitivity is low.