To provide a compact full observation device whose observation range can be changed in a height direction.

This device includes a window 101, a deflecting optical system 102 deflecting luminous flux taken in from the window 101, an aperture diaphragm 104 through which the luminous flux deflected by the optical system 102 passes, an image forming optical system 106 forming the luminous flux into an image, a rotating mechanism 10b rotating a bearing where the luminous flux is taken in from the window, an image rotation compensating means 105 compensating image rotation associated with the rotation of the bearing, and a lengthening and shortening mechanism 10c lengthening and shortening a distance between the optical systems 102 and 106. The optical system 106 has entrance pupils where a previously set viewing angle is obtained at two or more positions along the direction of an optical axis 2. The mechanism 10c moves the diaphragm 104 to any of the entrance pupil positions according as the distance is lengthened or shortened.