A projection display unit comprising: a projection optical system configured to project to a projection region on a projection surface, including: an illumination section, a projection lens, and a light valve; a light source section configured to emit invisible light for detection of an input operation along a detection light plane in proximity to the projection surface; a polarization separation device; and a detection optical system including a a zoom-out optical system and an image pickup device, wherein: the detection optical system is configured to detect whether the input operation is performed in a peripheral region outside the projection region on the projection surface, and in response to detection by the detection optical system in the peripheral region, a specific function is caused to be executed, wherein the detection optical system is further configured to capture a part of reflected light of the invisible light for detection of the input operation by the image pickup device through the projection lens and the polarization separation device, wherein the image pickup device is disposed in a position optically conjugating with the light valve, and wherein the light valve has a first rectangular shape and the image pickup device has a second rectangular shape, the second rectangular shape has a diagonal size d2 and the first rectangular shape has a diagonal size d1, wherein the following is met: d1 < β · d2, wherein β is the zoom-out magnification of the zoom-out optical system of the detection optical system. a projection optical system configured to project to a projection region on a projection surface, including: an illumination section, a projection lens, and a light valve; a light source section configured to emit invisible light for detection of an input operation along a detection light plane in proximity to the projection surface; a polarization separation device; and a detection optical system including a a zoom-out optical system and an image pickup device, an illumination section, a projection lens, and a light valve; a light source section configured to emit invisible light for detection of an input operation along a detection light plane in proximity to the projection surface; a polarization separation device; and a detection optical system including a a zoom-out optical system and an image pickup device, wherein: the detection optical system is configured to detect whether the input operation is performed in a peripheral region outside the projection region on the projection surface, and in response to detection by the detection optical system in the peripheral region, a specific function is caused to be executed, wherein the detection optical system is further configured to capture a part of reflected light of the invisible light for detection of the input operation by the image pickup device through the projection lens and the polarization separation device, wherein the image pickup device is disposed in a position optically conjugating with the light valve, and wherein the light valve has a first rectangular shape and the image pickup device has a second rectangular shape, the second rectangular shape has a diagonal size d2 and the first rectangular shape has a diagonal size d1, wherein the following is met: d1 < β · d2, wherein β is the zoom-out magnification of the zoom-out optical system of the detection optical system. the detection optical system is configured to detect whether the input operation is performed in a peripheral region outside the projection region on the projection surface, and in response to detection by the detection optical system in the peripheral region, a specific function is caused to be executed, wherein the detection optical system is further configured to capture a part of reflected light of the invisible light for detection of the input operation by the image pickup device through the projection lens and the polarization separation device, wherein the image pickup device is disposed in a position optically conjugating with the light valve, and wherein the light valve has a first rectangular shape and the image pickup device has a second rectangular shape, the second rectangular shape has a diagonal size d2 and the first rectangular shape has a diagonal size d1, wherein the following is met: d1 < β · d2, wherein β is the zoom-out magnification of the zoom-out optical system of the detection optical system.