An image formation lens (IL) is provided for forming the image of an observation object at a predetermined position by receiving a parallel light beam emitted from the observation object and exiting a microscope objective lens of infinity design. The image formation lens consists of a first lens group (G1) having positive refractivity and a second lens group (G2) having negative refractivity arranged sequentially from the object side. The first lens group (G1) consists of a positive lens (e.g. a double-convex lens (L1)) and a negative lens (e.g. a negative meniscus lens (L2)). The glass material of the positive and negative lenses constituting the first lens group (G1) satisfies the conditions of predetermined vdht and partial variance ratio Pht, and the glass material of all lenses has a transmissivity of 50% or above per 10 mm of glass thickness for the light having a wavelength of 340 nm, and 80% or above per 10 mm of glass thickness for the light having a wavelength of 360 nm.