To provide a projection type display device in which an optical system can be downsized without impairing conjugate relations between optical elements, and brightness, less uneven illuminance, and high contrast display are assured.

The projection type display device comprises an illuminating optical system 1, a reflection type light valve 2, and a projection optical system 3. The illuminating optical system 1 includes a light intensity uniformizing element 6, a relay lens group 7, a first mirror 8, and a second mirror 9. A luminous flux reflected on the second mirror 9 is made incident on the face of the reflection type light valve 2, which is to be illuminated. The second mirror 9 has an elliptical reflection face 9b. The lengthwise dimension S of the reflection type light valve 2, the long axial radius A and short axial radius B and eccentricity E of the ellipsoid 11, which define the elliptical reflection face 9b of the second mirror 9, establish the following relational formulas (1) to (3): A≥1.14×S...(1); B≥1.11×S...(2); E≥0.22×S...(3).