The bolometer-type THz wave detector according to the present invention has a thermal isolation structure in which a temperature detecting portion including a bolometer thin film connected to electrical wirings is supported in a state of being raised from the substrate by a supporting portion including the electrical wirings connected to a Read-out integrated circuit formed in a substrate, and the detector comprises a reflective film formed on the substrate, an absorbing film formed on the front surface or back surface or at an inner position in the temperature detecting portion , whereby an optical resonant structure is formed by the reflective film and the absorbing film, and a dielectric film formed on the reflective film. The dielectric film thickness f is set so that air gap between an upper surface of the dielectric film and a lower surface of the temperature detecting portion is smaller than 8 μm.