There is provided an exposure condition determining method for determining an exposure condition for an exposure-objective substrate having a plurality of semiconductor pattern features formed by predetermined exposure on a surface thereon, the method including, irradiating an illumination light onto a surface of a substrate, which has the pattern features, detecting a diffracted light from the plurality of semiconductor pattern features of the substrate irradiated with the illumination light, and determining the exposure condition based on a variation in brightness of the detected diffracted light.