A light source device of a projector adapted to irradiate blue light, red light, green light and yellow light in turn on an image-forming element and to form a color image on a screen (S) by the image-forming element , comprising: a light source section adapted to generate the blue light; a rotatable light path-switching disk which is disposed in a light path of the blue light and is adapted to periodically switch the light path of the blue light between a first light path and a second light path. a rotatable phosphor member disposed in the first light path and including a first phosphor (5a', 5a") adapted to generate green light or red light through irradiation of the blue light emitted from the light source section and a second phosphor adapted to generate yellow light through the irradiation of the blue light emitted from the light source section ; a dichroic mirror configured to combine light in the first light path with light in the second light path and direct the combined light to the image forming element ; a rotatable color-changing disk disposed between the dichroic mirror and the image forming element and adapted to select from the combined light any one of: the blue light emitted from the light source section , or the green light emitted either from the first phosphor (5a', 5a") or from the second phosphor , or the red light emitted either from the first phosphor (5a', 5a") or from the second phosphor , or the yellow light emitted from the second phosphor , and to irradiate the selected light to the image-forming element ; wherein the rotatable light path-switching disk and the rotatable color-changing disk rotate in synchronization at the same rotational speed. a light source section adapted to generate the blue light; a rotatable light path-switching disk which is disposed in a light path of the blue light and is adapted to periodically switch the light path of the blue light between a first light path and a second light path. a rotatable phosphor member disposed in the first light path and including a first phosphor (5a', 5a") adapted to generate green light or red light through irradiation of the blue light emitted from the light source section and a second phosphor adapted to generate yellow light through the irradiation of the blue light emitted from the light source section ; a dichroic mirror configured to combine light in the first light path with light in the second light path and direct the combined light to the image forming element ; a rotatable color-changing disk disposed between the dichroic mirror and the image forming element and adapted to select from the combined light any one of: the blue light emitted from the light source section , or the green light emitted either from the first phosphor (5a', 5a") or from the second phosphor , or the red light emitted either from the first phosphor (5a', 5a") or from the second phosphor , or the yellow light emitted from the second phosphor , and to irradiate the selected light to the image-forming element ; the blue light emitted from the light source section , or the green light emitted either from the first phosphor (5a', 5a") or from the second phosphor , or the red light emitted either from the first phosphor (5a', 5a") or from the second phosphor , or the yellow light emitted from the second phosphor , and to irradiate the selected light to the image-forming element ; wherein the rotatable light path-switching disk and the rotatable color-changing disk rotate in synchronization at the same rotational speed. <EOS>