PURPOSE: To provide an amphibian lens system capable of obtaining effective description performance in both of air and water only by arranging two lenses in the front of a lens system whose aberration is effectively corrected in air.

CONSTITUTION: The lens system is constituted of the 1st lens, the 2nd lens and a succeeding lens group arranged from the object side and the 1st and 2nd lenses have positive and negative or negative and positive refractive indexes and satisfies the following conditional expressions. Namely 10<νP-νN<60. 0.7<fN/fP<1.3 Provided that νP and νN is the Abbe numbers of the lenses having positive and negative refractive indexes out of the 1st and 2nd lenses and fP and fN are the focal distances of the lenses having positive and negative refractive indexes out of the 1st and 2nd lenses.