PURPOSE: To excellently compensate chromatic aberration and to considerably decrease a number of lens constitution in the read out lens system of a picture reader by arranging a specified lens composed of two lenses.

CONSTITUTION: This lens system is composed of a two lens composition of a first lens L1 having a positive refractive power and a second lens L2 in order from the object side. The first lens L1 is a radial type graded index lens (GRIN lens) having the distribution of refractive index in the radial direction from an optical axis. The shape of the first lens L1 has a negative refractive power, its medium has a positive refractive power and the refractive power of the whole lens L1 is positive. The second lens L2 is a positive meniscus lens whose concave surface confronts the object side. By adopting a GRIN lens, a number of lens constitution is considerably decreased and the chromatic aberration is excellently compensated although the lens system is composed of two simple lenses.