An image forming optical system comprises, in order from an object side, a first positive meniscus lens having a convex surface directed toward an object side, an aperture stop, a second positive meniscus lens having a convex surface directed toward the object side and a negative lens. At least one of surfaces of the negative lens is a spherical and the following condition is satisfied:

-2.0m/p0

-2.0(r1r+r2f)/(r1r-r2f)1.0

    • where m represents the power of the negative lens at the position of the maximum light height and p represents the power of the negative lens at the position of the near axis, r1r represents the radius of curvature of the first lens at the image side and r2f is the radius of curvature of the second lens at the object side.

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