A projection image display device includes: a laser light source; phosphor excited by excitation laser light emitted from laser light source to emit light; an optical functional reflector (cross dichroic prism) into which at least one laser light from laser light source and fluorescent light from phosphor enters and which reflects light of a specific wavelength band while transmitting light of the other wavelength band; a diffusion plate that diffuses the laser light; a diffusion plate driver for moving the diffusion plate; and a spatial light modulation element (digital micromirror device) that modulates the light output from cross dichroic prism. Diffusion plate is disposed on the optical path of excitation laser light applied from laser light source to phosphor.