PURPOSE: To provide an objective lens capable of exposing an optical master disk without any problem even when an optical source having a wavelength λ=200 to 300nm is used.

CONSTITUTION: The lens is provided with three lenses i.e., first, second and third lenses L1, L2 and L3, a front group having a negative refractive power as a whole and a back group consisting five lenses i,e., fourth to eighth lenses L4 to L8 having a positive refractive power as a whole. A back surface R2 of the lens L1 and the front surface R3 of the lens L2 are formed so that a positive meniscus shaped air lens whose concave surface faces the incident side is constructed between the lenses L1 and L2. Similarly, a back surface R8 of the lens L4 and a front surface R9 of the lens L5 are formed so that a positive meniscus shaped air lens whose concave surface faces the incident side is constructed between the lenses L4 and L5. Each lens is formed of quartz and these lenses are separated from each other by air gaps.