Disclosed is an image capturing optical system including, in order from an object side, a first lens having positive refractive power and concave upwards, a second lens having positive refractive power, a third lens having negative refractive power, a fourth lens having positive refractive power, a fifth lens having positive refractive power and including at least one inflection points on the object side or an upper surface, and a sixth lens having negative refractive power and being convex upwards.