As the diaphragm is stopped down, the width of two point sources that can be resolved from each other as two points (Rayleigh resolution limit/the radius of an airy disk) widens due to the influence of diffraction, which consequently makes it impossible to resolve a narrow width, thus causing an object image to become blurred. This phenomenon can be considered to be equivalent to that caused by an LPF effect. FIG. 4(A) is a graph illustrating a state of the width of two point sources that can be resolved from each other. In this graph, the horizontal axis represents the position (distance) on the light receiving surface and the vertical axis represents the light intensity. The width of two point sources that can be resolved from each other as two points (resolution width p between the two points) becomes narrower as the bell curve of the light intensity of each point source is steeper, while the width of two point sources that can be resolved from each other as two points (resolution width p between the two points) becomes wider as the bell curve of the light intensity of each point source is more gentle. For instance, in the case where the pixel pitch P of the image sensor 17 of the digital SLR camera 10 is approximately 6 μm, object images with the pixel pitch of P become impossible to be resolved if the diaphragm 13 is stopped down to f8. FIG. 4(B) shows the relationship between the aperture value and the Rayleigh resolution limit (resolution width between two points) p. In FIG. 4(B), the horizontal axis designates f-number (Fno) of the diaphragm and the vertical axis designates the Rayleigh resolution limit (p (μm)).