Provided is a method for acquiring an evaluation value that can suppress an influence caused by an orientation of an object to be evaluated on an evaluation value derived based on a phase image of the object to be evaluated. The method for acquiring an evaluation value includes generating a phase image showing a phase distribution of light transmitted through an object, deriving an evaluation value of the object based on the phase image, and correcting the evaluation value by using a correction coefficient determined in accordance with an orientation of the object in the phase image.