In a light source device, in each division of an image frame, two or more of the color lights X, Y and Z (e.g., red, green and blue) can be projected simultaneously. Each of the color lights X, Y and Z is divided into two in terms of time so that synthesized light of one group of division color lights enters a first spatial modulation element. Synthesized light of another group of division color lights enters a second spatial modulation element, whereby gradation of each color light in each of the first and second spatial modulation elements is controlled.