To provide a compact telecentric optical system, etc., having a comparatively long operating distance, with high-specification.

The optical system is provided with negative, positive and positive lens groups G1, G2 and G3, in this order from an enlargement side, the group G1 is provided with a positive lens L11 and a negative lens L13, the positive lens L11 is a biconvex lens, and the negative lens L13 is formed into a meniscus shape, so that the surface having the small curvature radius faces a reduction side. Also the group G2 is provided with a positive lens L21 and an achromatic lens component, whose concave faces the reduction side, and the positive lens L21 is formed, so that the surface having the large curvature radius faces the enlargement side. The group G3 is constituted of a positive sub lens group G31 and a positive sub lens group G32, in this order from the enlargement side, the group G31 is provided with a positive lens L31, and the positive sub lens group G32 is provided with a positive achromatic lens, a negative lens L34 and a positive lens L35.