To propose a polarization illuminating device capable of realizing miniaturization without lowering the utilization efficiency of light, and a projection type display device using the illuminating device.

In the polarization illuminating device 2 of the projection type display device; emitted light from a light source part 21 is allowed to pass through a variable angle prism 22 so that luminous flux width may be narrowed, and then it is made incident on a prism beam splitter 23, where it is separated to P polarized light and S polarized light. The separating direction is the direction of the narrowed luminous flux width (Lw1 and Lw2). After arranging the direction of polarization, the polarized light passes through an integrator optical system 27 to be made a uniform light source, and irradiates a liquid crystal light valve. Since the luminous flux width of the light source is narrowed by the prism 22, the width of the beam splitter 23 is made small and the increase of the luminous flux width caused by the separation of the polarized light in the beam splitter 23 is restrained. Therefore, the device is miniaturized. Since the luminous flux width of the light source is not wide, the light is effectively utilized even when a small projection lens is used and a bright projected video is obtained.