To provide an LED illumination light source for a projector in simple constitution, which does not require space for condensing light and radiating heat.

The light source device 20 is constituted of: an LED 21; a heat radiation substrate 22 made of aluminum on which the LED 21 is fixed; and a hollow rod 23 made of aluminum to which the heat radiation substrate 22 is attached. The LED 21 includes LED chips of three colors R, G and B. The hollow rod 23 is a tubular member whose both ends are made open, and is equipped with: a tube part 24 having an inner wall surface where four reflection surfaces 25 mirror-finished are arranged to be rectangular so as to face each other, the tube part 24 in which slender space (light tunnel) having a rectangular cross section is formed; openings 27 and 28 formed on both ends; and a flange part 30. The heat radiation substrate 22 is fixed to the flange part 30 such that the fixed LED 21 is at the center of the hollow rod 23, and covers the opening 27.