A projection display unit includes a projection optical system, a polarization separation device, and a detection optical system. The projection optical system includes an illuminator, a projection lens, and a light valve. The light valve modulates illumination light supplied from the illuminator on a basis of an image signal, and outputs the modulated illumination light toward the projection lens. The polarization separation device is disposed between the light valve and the projection lens. The polarization separation device separates entering light into a first polarized component and a second polarized component, and outputs the first polarized component and the second polarized component in respective directions that are different from each other. The detection optical system includes an imaging device. The imaging device is disposed in a position that is optically conjugate to a position of the light valve, and receives, via the projection lens and the polarization separation device, light based on invisible light applied along a plane in vicinity of the projection surface. The following conditional expression (1): d1