In the case where RGB light emitting elements are used as light sources of a surface emitting type illumination device, the occurrence of color irregularity in the vicinity of a light incident surface is prevented, so that uniform white light is obtained on an entire light outgoing surface. In a light source device including light emitting elements of respective colors including red light emitting elements, green light emitting elements, and blue light emitting elements that emit light in a red (R) wavelength range, light in a green (G) wavelength range, and light in a blue (B) wavelength range, respectively, the light emitting elements being provided on one principal surface of a substrate, the light emitting elements of the respective colors are aligned in a longitudinal direction of the substrate, the number of the green light emitting elements is larger than the number of each of the red light emitting elements and the blue light emitting elements, and the light emitting elements of the respective colors in the longitudinal direction of the substrate are aligned at regular Intervals for each of the colors.