PURPOSE: To forbid the movement of an image point even if a lens inclines by forming the whole or part of at least one face of the lens, whose faces is not required to be passed with rays, to a spherical shape so that the center of curvature of the spherical phase coincides with the nodal point of the lens.

CONSTITUTION: The single lens 1 is formed to the spherical shape in the whole or part of at least one face of the lens, whose face is not required to be passed with rays, so that the center of the curvature of this spherical phase is made to coincide with the nodal point 10 of the lens. Even if, therefore, the lens inclines, the nodal point 10 does not move as the contact part of a lens barrel 2 and the lens 1 constitutes the spherical phase around the nodal point 10 of the lens 1. The incident rays on the lens 1 toward the nodal point 10 thereof do not change the direction thereof. The image point is, therefore, formed at the position based on the lens barrel 2 even if the lens 1 is mounted with an inclination to the lens barrel 2 when the lens 1 is inserted and fixed into the barrel 2. The adjustment for mounting is thus exceedingly facilitated.