An illumination optical system for a beam projector comprising: at least one light source for generating a light; a color conversion unit having a reflective layer that reflects light emitted from the at least one light source and a fluorescent substance layer that converts a wavelength of the light emitted from the at least one light source to a wavelength-converted light; and at least one dichroic mirror disposed at a predetermined angle with respect to the at least one light source, for deflecting the light emitted from the at least one light source to be incident on the color conversion unit, characterised in that: wherein the at least one light source is a laser diode that produces a blue laser light, and the dichroic mirror comprises: a first reflective area for reflecting the blue laser light to be incident on the color conversion unit; a second reflective area formed around the first reflective area for reflecting the blue laser light to be incident on the color conversion unit; and a transmissive area formed between the first reflective area and the second reflective area for transmitting the blue laser light reflected by the reflective layer of the color conversion unit. at least one light source for generating a light; a color conversion unit having a reflective layer that reflects light emitted from the at least one light source and a fluorescent substance layer that converts a wavelength of the light emitted from the at least one light source to a wavelength-converted light; and at least one dichroic mirror disposed at a predetermined angle with respect to the at least one light source, for deflecting the light emitted from the at least one light source to be incident on the color conversion unit, characterised in that: wherein the at least one light source is a laser diode that produces a blue laser light, and the dichroic mirror comprises: a first reflective area for reflecting the blue laser light to be incident on the color conversion unit; a second reflective area formed around the first reflective area for reflecting the blue laser light to be incident on the color conversion unit; and a transmissive area formed between the first reflective area and the second reflective area for transmitting the blue laser light reflected by the reflective layer of the color conversion unit. wherein the at least one light source is a laser diode that produces a blue laser light, and the dichroic mirror comprises: a first reflective area for reflecting the blue laser light to be incident on the color conversion unit; a second reflective area formed around the first reflective area for reflecting the blue laser light to be incident on the color conversion unit; and a transmissive area formed between the first reflective area and the second reflective area for transmitting the blue laser light reflected by the reflective layer of the color conversion unit. a first reflective area for reflecting the blue laser light to be incident on the color conversion unit; a second reflective area formed around the first reflective area for reflecting the blue laser light to be incident on the color conversion unit; and a transmissive area formed between the first reflective area and the second reflective area for transmitting the blue laser light reflected by the reflective layer of the color conversion unit.