An illumination optical system, comprising: a laser light source that generates an excitation light having a first wavelength (λ 1); a phosphor wheel comprising a blue fluorescent light generation region (105 1) that generates fluorescent light having a second wavelength (λ 2) by means of the excitation light, a green fluorescent light generation region (105 2,105 4) that generates fluorescent light having a third wavelength (λ 3) by means of the excitation light, and a transparent region (105 3) opposed to the blue fluorescent light generation region that allows excitation light to pass therethrough; an LED light source that generates light having a fourth wavelength (λ 4) longer than the first, second and third wavelenght; a recursive mechanism (110 1, 110 2) that causes excitation light that has passed through the transparent region (105 3) to be incident from the opposite side of the phosphor wheel on the blue fluorescent light generation region; and dichroic mirrors (103, 104) that reflect fluorescent light having the second wavelength (λ 2) and the third wavelength (λ 3), and allows light having the fourth wavelength (λ 4) to pass therethrough to thereby emit each of the lights in the same direction; wherein the dichroic mirrors (103, 104) comprise: a first dichroic mirror in front of the phosphor wheel that reflects in said direction fluorescent light having the third wavelength (λ 3) that is generated when the excitation light is incident on the green fluorescent light generation region (105 2); and a second dichroic mirror, parallel to the first dichroic mirror, that reflects in said direction fluorescent light having the second wavelength (λ 2) that is generated when the excitation light that passes through the transparent region (105 3) is incident on the blue fluorescent light generation region (105 1) by means of the recursive mechanism (110 1, 110 2). a laser light source that generates an excitation light having a first wavelength (λ 1); a phosphor wheel comprising a blue fluorescent light generation region (105 1) that generates fluorescent light having a second wavelength (λ 2) by means of the excitation light, a green fluorescent light generation region (105 2,105 4) that generates fluorescent light having a third wavelength (λ 3) by means of the excitation light, and a transparent region (105 3) opposed to the blue fluorescent light generation region that allows excitation light to pass therethrough; an LED light source that generates light having a fourth wavelength (λ 4) longer than the first, second and third wavelenght; a recursive mechanism (110 1, 110 2) that causes excitation light that has passed through the transparent region (105 3) to be incident from the opposite side of the phosphor wheel on the blue fluorescent light generation region; and dichroic mirrors (103, 104) that reflect fluorescent light having the second wavelength (λ 2) and the third wavelength (λ 3), and allows light having the fourth wavelength (λ 4) to pass therethrough to thereby emit each of the lights in the same direction; wherein the dichroic mirrors (103, 104) comprise: a first dichroic mirror in front of the phosphor wheel that reflects in said direction fluorescent light having the third wavelength (λ 3) that is generated when the excitation light is incident on the green fluorescent light generation region (105 2); and a second dichroic mirror, parallel to the first dichroic mirror, that reflects in said direction fluorescent light having the second wavelength (λ 2) that is generated when the excitation light that passes through the transparent region (105 3) is incident on the blue fluorescent light generation region (105 1) by means of the recursive mechanism (110 1, 110 2). a first dichroic mirror in front of the phosphor wheel that reflects in said direction fluorescent light having the third wavelength (λ 3) that is generated when the excitation light is incident on the green fluorescent light generation region (105 2); and a second dichroic mirror, parallel to the first dichroic mirror, that reflects in said direction fluorescent light having the second wavelength (λ 2) that is generated when the excitation light that passes through the transparent region (105 3) is incident on the blue fluorescent light generation region (105 1) by means of the recursive mechanism (110 1, 110 2).