A method for generating an image restoration filter used to correct a deterioration of an image captured through an optical system includes a first step of setting a target restoration gain value representative of a target restoration degree of an absolute value of an optical transfer function of the optical system, within a restoration gain limiting value calculated by dividing a maximum value operable by a fixed-point arithmetic by a data point number of the optical transfer function, and a second step of generating, through the fixed-point arithmetic, a frequency characteristic of the image restoration filter based on the target restoration gain value set by the first step.