A terahertz band filter for filtering, in a frequency band, a terahertz wave propagating between a pair of metal plates with an upper parallel surface facing a lower parallel surface includes a sheet parallel to the upper and lower parallel surfaces, which is disposed between the metal plates and is spaced apart therefrom, and at least one slit located in the sheet to face the upper and lower parallel surfaces, wherein the sheet comprises a single slit to function as a notch filter for blocking in a specific frequency band.