A stereo camera unit which enables the three-dimensional (3D) image acquisition using conventional two-dimensional (2D) rigid endoscopes is proposed. It consists of an afocal optical system, a beam splitter, and two cameras. The exit pupil of the endoscope, which exists in the proximity of the eyepiece, is optically transferred to a different position. The beam splitter divides the transferred exit pupil into two identical exit pupils, where the entrance pupils of the two cameras are located. The proposed technique provides a low-cost solution for the construction of 3D endoscopes, because conventional 2D endoscopes can be used and the stereo camera unit can be constructed using off the shelf devices. The preliminary experiments were conducted to verify the proposed technique. The evaluation of the resolution, the subjective evaluation, and task efficiency of 3D images are shown.