To provide an optical device which can be made compact in the whole device, in which accuracy of disposing each optical surface can be fixed to a high level without adjusting the position upon assembling, and fluorescent light, emission light, illumination light or the like can be condensed into a minute region at high efficiency.

The optical device includes a transparent plate-type column body 1. The side faces have quadratic surfaces 13a, 13b the cross-sectional shapes of which in the longitudinal direction show two kinds of quadratic curves opposing to each other with convexes facing outward, having the same reference point P and asymmetry with respect to a common axis AX passing over the reference point. The upper face 13c and the bottom face 13d are flat planes parallel to each other; and the upper face includes a recess 4 for holding a light emitting body close to the reference point. The surface of the column body reflects internal light and includes a transmitting portion 15 close to the axis AX on one of the quadratic surfaces 13a, 13b for transmitting the internal light of the plate type column body 1.