A dielectric boundary surface estimation device comprising: a pre-processing unit pre-processing wave data obtained by observing a dielectric by a radar device; a three-dimensional synthetic aperture processing unit performing three-dimensional synthetic aperture processing on the wave data pre-processed by the pre-processing unit; and a dielectric boundary surface estimating unit estimating a boundary surface (41, 42) between areas having different dielectric constants to each other using the wave data on which the three-dimensional synthetic aperture processing is performed by the three-dimensional synthetic aperture processing unit and calculating a width (Δx, Δy) and a thickness (Δz) of the boundary surface, wherein the dielectric boundary surface estimating unit performs aperture division of the wave data on which the three-dimensional synthetic aperture processing unit performs the three-dimensional synthetic aperture processing, by dividing the wave data by N in an azimuth direction and by M in an elevation direction, performs three-dimensional inverse Fourier transform on the wave data after the division, obtains a set of local minimum points of the wave data smaller than a threshold as a locus of low-dielectric constant side boundary points corresponding to a low-dielectric constant side boundary surface, from the wave data after the division subjected to the three-dimensional inverse Fourier transform, and obtains a set of local maximum points of the wave data exceeding the threshold as a locus of high-dielectric constant side boundary points corresponding to a high-dielectric constant side boundary surface from the wave data after the division subjected to the three-dimensional inverse Fourier transform, calculates a width of the high-dielectric constant side boundary surface or a width of the low-dielectric constant side boundary surface from the locus of the high-dielectric constant side boundary points or the locus of the low-dielectric constant side boundary points, and calculates a thickness from the high-dielectric constant side boundary surface to the low-dielectric constant side boundary surface on a basis of a distance between a center of the locus of the high-dielectric constant side boundary points and a center of the locus of the low-dielectric constant side boundary points. a pre-processing unit pre-processing wave data obtained by observing a dielectric by a radar device; a three-dimensional synthetic aperture processing unit performing three-dimensional synthetic aperture processing on the wave data pre-processed by the pre-processing unit; and a dielectric boundary surface estimating unit estimating a boundary surface (41, 42) between areas having different dielectric constants to each other using the wave data on which the three-dimensional synthetic aperture processing is performed by the three-dimensional synthetic aperture processing unit and calculating a width (Δx, Δy) and a thickness (Δz) of the boundary surface, wherein the dielectric boundary surface estimating unit performs aperture division of the wave data on which the three-dimensional synthetic aperture processing unit performs the three-dimensional synthetic aperture processing, by dividing the wave data by N in an azimuth direction and by M in an elevation direction, performs three-dimensional inverse Fourier transform on the wave data after the division, obtains a set of local minimum points of the wave data smaller than a threshold as a locus of low-dielectric constant side boundary points corresponding to a low-dielectric constant side boundary surface, from the wave data after the division subjected to the three-dimensional inverse Fourier transform, and obtains a set of local maximum points of the wave data exceeding the threshold as a locus of high-dielectric constant side boundary points corresponding to a high-dielectric constant side boundary surface from the wave data after the division subjected to the three-dimensional inverse Fourier transform, calculates a width of the high-dielectric constant side boundary surface or a width of the low-dielectric constant side boundary surface from the locus of the high-dielectric constant side boundary points or the locus of the low-dielectric constant side boundary points, and calculates a thickness from the high-dielectric constant side boundary surface to the low-dielectric constant side boundary surface on a basis of a distance between a center of the locus of the high-dielectric constant side boundary points and a center of the locus of the low-dielectric constant side boundary points.