An illuminating unit having a plurality of light emitting devices and collimators and a projection type image display apparatus using the same are provided. The illuminating unit includes: a plurality of light emitting devices which output light beams of predetermined wavelengths; a plurality of collimators, each having a parabolic reflection surface for reflecting the light beam in a predetermined direction, a mounting section for locating the light emitting device at the focal point of the parabolic reflection surface, a light output surface opposite to the parabolic reflection surface, and a light guide section for guiding the light beam reflected from the parabolic reflection surface to the light output surface; and one or more fixing members having two or more steps for mounting the light emitting devices and the collimators on their top surface. A plurality of light emitting devices and collimators are efficiently arranged in a small space. Therefore, thermal concentration can be reduced and heat can be effectively discharged.