To achieve uniform irradiation by a single light source and to also achieve miniaturization and wt. reduction, by allowing light to be incident on a light transmitting medium such as wedge-shaped plastic to closely bond an electrophoretic gel plate to the surface of the light transmitting medium and placing a black plate under the medium to observe the pattern of the gel plate.

A viewer is constituted of a light transmitting medium 1 being a wedge shaped lump of a transparent material such as plastic or the like, a light incident surface 2 and a light source 3, a gel plate 4 is placed on the upper surface 7 of the medium 1, water 6 is dripped on the plate 4 to closely bond the plate 4 to the upper surface 7 so as not to generate irregular reflection, and a black plate 5 is arranged under the rear surface of the medium 1. When the incidence surface 2 is irradiated by using a fluoresent lamp 3, light is totally reflected to propagate through the wedge-shaped lump. Herein, when a gel is observed, since the gel is closely bonded to a light emitting element and the rear surface itself of the light emitting element can be brought to a black surface, the stripe like arrangement of the stripes of the white parts and transparent parts of the gel can be observed in good contrast. Since the black plate 5 constitutes a surface or is closely bonded, a viewer can be compactly constituted to be reduced in wt. and size.