In a light source device, that obtains high light usage efficiency by projecting simultaneously two or more of three primary color lights X, Y and Z. Moreover, each color light X, Y and Z is divided into two in terms of time so that p-wave and s-wave linear polarization lights are formed, such that the synthesized light of the p-wave linear polarization lights enters a first spatial modulation element and the synthesized light of the s-wave linear polarization lights enters a second spatial modulation element to permit gradation control of each color light.