This paper proposes a simple and novel singlecamera depth estimation method using images reflected by a single transparent parallel planar plate. The transparent plate reflects and transmits the incident light on its surface. The transmitted light is then reflected on the rear-surface and is transmitted again to the air through the surface. These two light paths create an overlapped image that comprises two shifted images. The overlapped image is considered as a stereo image obtained from a narrow baseline stereo. The constraint of these stereo images is presented. The distance to the object can be derived by finding correspondences on the constraint lines using the autocorrelation function of the overlapped image. This paper presents experimental results obtained using an actual system with a transparent acrylic plate.