PURPOSE: To obtain an observation device having wide visual sensation of a half viewing angle of about 90° without having an intricate lens system by arranging plural observation systems on a curved surface of a lens having a large aberration in the curvature of field.

CONSTITUTION: The lens 1 capable of forming the images from a visual field of the high viewing angle is provided with the aberration in the curvature of field, etc., to converge luminous fluxes to the curved surface having a curved shape. This curved surface is used as the observation surface. The luminous flux made incident at, for example, the arbitrary half viewing angle G2 is imaged at the point P2 on the circumference of the circle around the lens 1. Similarly, the luminous fluxes from all the viewing angles are imaged at the points P0, P1,... on the same circumference up to about, for example, the max. half viewing angle of 90°. Namely, the observation surface is not limited to one plane and is formed as the curved surface. The optical design of such lens 1 is made possible by making the design to extremely degrade only the aberration in the curvature of field. The plural observation systems are arranged on the curved surface of the concentrical circle or the curved surface curved to the arbitrary shape, by which the function to observe and measure the object image up to the extremely high viewing angle or the visual field information at one time is made executable.