1. A non-transitory computer-readable storage medium storing a program that causes a computer to decide an exposure condition in an exposure apparatus including an illumination optical system for illuminating a mask, and a projection optical system for projecting an image of a pattern of the mask onto a substrate, the program causing the computer to execute: a first step of selecting an evaluation item of interest that is an evaluation item on which focus is to be placed from a plurality of evaluation items to be used to evaluate an image formed on an image plane of the projection optical system in correspondence with the exposure condition in comparison with a target pattern to be formed on the substrate; a second step of selecting, as an auxiliary evaluation item, an evaluation item from the plurality of evaluation items which is different from the evaluation item of interest and changes a value in the same direction as that of a change in a value of the evaluation item of interest upon changing parameter values included in the exposure condition; a third step of setting an evaluation function including the evaluation item of interest and the auxiliary evaluation item as values; a fourth step of changing the parameter values so as to make a value of the evaluation function closer to a target value and calculating the value of the evaluation function for each of a plurality of images formed on the image plane of the projection optical system in correspondence with the parameter values; and a fifth step of deciding, as the parameter values included in the exposure condition, parameter values corresponding to a value of the evaluation function satisfying the target value out of the plurality of values of the evaluation function calculated in the fourth step.