An optical element comprising: a first optical layer having a concave-convex surface; a wavelength-selective reflection layer formed on the concave-convex surface; and a second optical layer formed on the wavelength-selective reflection layer, wherein the wavelength-selective reflection layer has a five-layer structure in which a high-refractive-index layer and a metal layer are alternately stacked, and in the case when the entire wavelength-selective reflection layer has a geometric film thickness L of 80 nm, a ratio α = d b /d a of an optical film thickness d b of the entire metal layer relative to an optical film thickness d a of the entire high-refractive-index layer and a ratio β = d 3 /d 1 of an optical film thickness d 3 of the third high-refractive-index layer relative to an optical film thickness d 1 of the first high-refractive-index layer, when viewed from either the first optical layer side or the second optical layer side, are included in a first region surrounded by the following formulas to, whereas in the case when the entire wavelength-selective reflection layer has a geometric film thickness L of 90 nm, the ratio α and the ratio β are included in a second region surrounded by the following formulas to, and wherein in the case when the entire wavelength-selective reflection layer has a geometric film thickness L of 80 nm < L < 90 nm, supposing that each of minute sides formed by dividing a periphery C1 of the first region into n-equal portions, with an intersection between the formula and formula being set as a starting point, is represented as Δ C1i where i denotes an integer between 0 and n, both inclusive, and that each of minute sides formed by dividing a periphery C2 of the second region into n-equal portions, with an intersection between the formula and formula being set as a starting point, is represented as Δ C2i, and that each of minute regions having a rectangular shape, with Δ C1i and Δ C2i being formed as the two short sides, is defined as Δ Si, the ratio α and the ratio β are surrounded by a circumferential surface S composed of a group of minute regions Δ Si wherein formulae - are the following equalities α = − 0.0004 β 2 + 0.0053 β + 0.0065 α = − 1 × 10 − 5 β 2 + 0.0007 β + 0.0066 α = − 1 × 10 − 5 β 2 + 0.0005 β + 0.0119 α = 0.012114 α = − 0.0002 β 2 + 0.0039 β + 0.0087 α = − 3 × 10 − 5 β 2 + 0.0014 β + 0.0038 α = − 2 × 10 − 5 β 2 + 0.0006 β + 0.0112 α = 0.010589 a first optical layer having a concave-convex surface; a wavelength-selective reflection layer formed on the concave-convex surface; and a second optical layer formed on the wavelength-selective reflection layer, wherein the wavelength-selective reflection layer has a five-layer structure in which a high-refractive-index layer and a metal layer are alternately stacked, and in the case when the entire wavelength-selective reflection layer has a geometric film thickness L of 80 nm, a ratio α = d b /d a of an optical film thickness d b of the entire metal layer relative to an optical film thickness d a of the entire high-refractive-index layer and a ratio β = d 3 /d 1 of an optical film thickness d 3 of the third high-refractive-index layer relative to an optical film thickness d 1 of the first high-refractive-index layer, when viewed from either the first optical layer side or the second optical layer side, are included in a first region surrounded by the following formulas to, whereas in the case when the entire wavelength-selective reflection layer has a geometric film thickness L of 90 nm, the ratio α and the ratio β are included in a second region surrounded by the following formulas to, and wherein in the case when the entire wavelength-selective reflection layer has a geometric film thickness L of 80 nm < L < 90 nm, supposing that each of minute sides formed by dividing a periphery C1 of the first region into n-equal portions, with an intersection between the formula and formula being set as a starting point, is represented as Δ C1i where i denotes an integer between 0 and n, both inclusive, and that each of minute sides formed by dividing a periphery C2 of the second region into n-equal portions, with an intersection between the formula and formula being set as a starting point, is represented as Δ C2i, and that each of minute regions having a rectangular shape, with Δ C1i and Δ C2i being formed as the two short sides, is defined as Δ Si, the ratio α and the ratio β are surrounded by a circumferential surface S composed of a group of minute regions Δ Si wherein formulae - are the following equalities α = − 0.0004 β 2 + 0.0053 β + 0.0065 α = − 1 × 10 − 5 β 2 + 0.0007 β + 0.0066 α = − 1 × 10 − 5 β 2 + 0.0005 β + 0.0119 α = 0.012114 α = − 0.0002 β 2 + 0.0039 β + 0.0087 α = − 3 × 10 − 5 β 2 + 0.0014 β + 0.0038 α = − 2 × 10 − 5 β 2 + 0.0006 β + 0.0112 α = 0.010589