A light source device comprising: a light source section configured to emit blue excitation light; a phosphor configured to generate red fluorescent light and green fluorescent light through irradiation of the excitation light emitted from the light source section; a color-changing section comprising a rotatable color-changing disk comprising: a first transmitting area configured to transmit blue color light and block the transmission of red and green fluorescent light, a second transmitting area configured to transmit yellow fluorescent light and block the transmission of blue color light, wherein the yellow fluorescent light isfrom the red and green fluorescent light emitted from the phosphor, a third transmitting area configured to transmit green fluorescent light and block the transmission of blue color light and red fluorescent light, and a fourth transmitting area configured to transmit red fluorescent light and block the transmission of blue color light and green fluorescent light; and a light path-switching section disposed in a light path of the light emitted from the light source section, and configured to switch a light path of the light emitted from the light source section between a first light path in which the blue excitation light emitted from the light source section passes towards the phosphor and a second light path in which the blue excitation light emitted from the light source section passes towards the first transmitting area of the color-changing disk, wherein the light path-switching section comprises a light path-switching disk comprising a reflecting area configured to direct the blue excitation light emitted from the light source section on the first light path, and a transmitting area configured to direct the blue excitation light emitted from the light source section on the second light path; wherein the phase of a boundary between the reflecting area and the transmitting area of the light path-switching disk and the phase of a boundary between the first transmitting area and the second transmitting area of the color-changing disk rotate in synchronization, and wherein the light source section is configured to turn off when a beam spot incident on the color-changing disk is on a boundary which is before or after a transmitting area (10e, 10f) configured to transmit a lowest amount of light among all transmitting areas of the color-changing disk. a light source section configured to emit blue excitation light; a phosphor configured to generate red fluorescent light and green fluorescent light through irradiation of the excitation light emitted from the light source section; a color-changing section comprising a rotatable color-changing disk comprising: a first transmitting area configured to transmit blue color light and block the transmission of red and green fluorescent light, a second transmitting area configured to transmit yellow fluorescent light and block the transmission of blue color light, wherein the yellow fluorescent light isfrom the red and green fluorescent light emitted from the phosphor, a third transmitting area configured to transmit green fluorescent light and block the transmission of blue color light and red fluorescent light, and a fourth transmitting area configured to transmit red fluorescent light and block the transmission of blue color light and green fluorescent light; and a first transmitting area configured to transmit blue color light and block the transmission of red and green fluorescent light, a second transmitting area configured to transmit yellow fluorescent light and block the transmission of blue color light, wherein the yellow fluorescent light isfrom the red and green fluorescent light emitted from the phosphor, a third transmitting area configured to transmit green fluorescent light and block the transmission of blue color light and red fluorescent light, and a fourth transmitting area configured to transmit red fluorescent light and block the transmission of blue color light and green fluorescent light; and a light path-switching section disposed in a light path of the light emitted from the light source section, and configured to switch a light path of the light emitted from the light source section between a first light path in which the blue excitation light emitted from the light source section passes towards the phosphor and a second light path in which the blue excitation light emitted from the light source section passes towards the first transmitting area of the color-changing disk, wherein the light path-switching section comprises a light path-switching disk comprising a reflecting area configured to direct the blue excitation light emitted from the light source section on the first light path, and a transmitting area configured to direct the blue excitation light emitted from the light source section on the second light path; wherein the phase of a boundary between the reflecting area and the transmitting area of the light path-switching disk and the phase of a boundary between the first transmitting area and the second transmitting area of the color-changing disk rotate in synchronization, and wherein the light source section is configured to turn off when a beam spot incident on the color-changing disk is on a boundary which is before or after a transmitting area (10e, 10f) configured to transmit a lowest amount of light among all transmitting areas of the color-changing disk.