An optical unit includes a light source unit emitting parallel light; a light-receiving element array; and a prism rendering emitted light from the light source unit incident on a specimen placement section and introducing totally reflected light from the specimen placement section into the light-receiving element array. The prism has an entrance surface rendering the parallel light emitted from the light source unit incident on the prism, a curved reflecting surface which reflects light passing through the entrance surface and incident on the prism toward a focal position thereof, the specimen placement section of a planar shape provided at a position including the focal position of the curved reflecting surface, and an exit surface making light totally reflected at the focal position of the curved reflecting surface in the specimen placement section emerge into the outside of the prism.