To provide a light source device for a projector which efficiently radiates heat generated by an LED for a light source in simple constitution suitable for miniaturization and thinning.

The light source device comprises: a rotating member 24 which rotates by using a motor; a plurality of blade plates 25 which are arranged on the rotating member 24 at equal intervals; a ring member 26 and a coupling ring 27 which are configured to successively provide the plurality of blade plates 25; a plurality of LEDs 30 which are arranged between two adjacent blade plates 25 and fixed on an outer circumferential surface 28 of the ring member 26; and a condensing lens 32 which is fixed to a case 21. A suction port 34 is provided on an upper surface of the case 21 and an exhaust port 35 is provided on a side surface thereof, and an air duct 37 is provided between a cooling plate 36 of a DMD 15 and the exhaust port 35. The plurality of blade plates 25 rotate to suck air from the suction port 34 and send it out toward the outside from the inside. The air sent out is discharged from the exhaust port 35, and made to blow to the cooling plate 36 through the air duct 37.