To obtain the optical low-pass filter which has a ≤0.10 MTF value by making the cycle, width, and height of a rectangular wave, and the refractive index of an atmosphere and the refractive index of a filter base material against specific wavelength light meet specific conditions.

The cycle of the rectangular wave is denoted as T (μm), the width as a (μm), the height as d (nm), the refractive index of the atmosphere to the light of 550 nm wavelength as n1, and the refractive index of the filter base material to the light of 550 nm wavelength as n2. Here, conditions of at least either of 0.225≤(a/T)≤0.425 and 0.3<n1-n2≤0.7, and Y1≤(a/T)n1-n2d≤Y2 are met. Here, Y1=18067(a/T)3-19350(a/T)2+7399(a/T)-868, and Y2=733(a/T)3-990(a/T)2+924(a/T)-98. Namely, a superior low-pass correcting function to light of about 550 nm wavelength can be displayed.