Provided is a dental observation device by which without displaying, in an overlapping manner, a visible light image of a desired image-capturing site in an oral cavity region captured by a three-dimensional camera and three-dimensional image information on the desired image-capturing site in the oral cavity region acquired in advance, an invisible portion in the visible light image is easily recognized. An observation system 3 includes a visible light three-dimensional camera 52 performing three-dimensional image capturing of a two-dimensional captured image P of a surgical operation target site in an oral cavity region； a relative position calculator 12 detecting an image-capturing direction of the visible light three-dimensional camera 52 with respect to the surgical operation target site； a three-dimensional information storage 31 storing three-dimensional image information acquired in advance； an image display portion 110 displaying, side by side, a two-dimensional captured image P captured by the visible light three-dimensional camera 52 and two-dimensional converted image Cs based on the three-dimensional image information corresponding to the surgical operation target site； and a display direction adjuster 13 displaying, in the image display portion 110, the two-dimensional converted image Cs in a predetermined direction on the basis of the image-capturing direction detected by the relative position calculator 12.
