A projection type image display apparatus using a light source where excitatory light makes fluorescent material to emit fluorescent light is provided with improved lifetime of a fluorescent material light source without increasing in the apparatus size, The apparatus comprises an excitatory light source cluster, a substrate on which fluorescent material is arranged, light intensity detectors measuring the intensities of the excitatory light and the fluorescent light, a control device which judges based on the measured values of the light intensity detectors whether or not to move the substrate, and a motion device which moves the substrate. The control device may issue an instruction to move the substrate when the ratio of the decrease in the fluorescent light intensity to that in the excitatory light intensity exceeds a prescribed value. Also, the substrate may be moved in a direction perpendicular to the direction of the excitatory light optical axis.