A light source optical system includes a wavelength conversion unit configured to receive first color light emitted from by an excitation light source and emit second color light with a wavelength different from a wavelength of the first color light; and a first optical system and a second optical system provided in an optical path between the excitation light source and the wavelength conversion unit. The first optical system includes one optical element having a negative power, wherein the second optical system as a whole has a positive power, and wherein Conditional Expression (1) is satisfied as follows: 1.8