To provide a far-infrared camera lens which is mounted on a vehicle, is small and inexpensive, and has a wide angle of view of 50 to 70 and to provide a lens unit and an imaging apparatus which use this lens.

Three lenses formed of ZnS are used in combination. A first lens is a meniscus lens having a middle portion which is convex on an object side. A second lens has a middle portion that is a meniscus, which is concave on an object side and has positive refractive power, and a peripheral portion, which is convex on the object side. The first and second lenses have positive refractive power in combination. A third lens is provided adjacent to the second lens with a distance therebetween 1 mm or less and has a middle portion, which is a convex meniscus on an object side, and a peripheral portion which is concave on the object side. A diffraction surface is formed in either surface of the lens. The total focal distance f of the lens system is 6 to 11 mm. The focal distances f12 of the first and second lenses are 5 to 18 mm, and there is a limit of 0.9f12/f1.6.