An image projection apparatus for projecting an image, comprising an optical system comprising: a light source ; an optical element comprising a total internal reflection prism unit configured to transmit and reflect light emitted from the light source; and an optical modulation element configured to switch between a first mode and a second mode in order to modulate light incident on the optical modulation element based on image data, wherein in the first mode, the optical modulation element is configured to receive the light transmitted and reflected from the optical element and reflect first light rays , as ON light for forming an image based on image data, in a first direction, and in the second mode, the optical modulation element is configured to receive the light transmitted and reflected from the optical element and reflect second light rays , as OFF light not for forming an image, in a second direction different from the first direction, wherein the second light rays reflected from the optical modulation element travel on an opposite side of the first light rays reflected from the optical modulation element across the light received by the optical modulation element , the total internal reflection prism unit has an interface (B) that transmits the first light rays to be directed to a projection target for forming the image, and characterised in that the interface (B) reflects the second light rays and the light emitted from the light source to be directed to a position different from the position of the projection target. a light source ; an optical element comprising a total internal reflection prism unit configured to transmit and reflect light emitted from the light source; and an optical modulation element configured to switch between a first mode and a second mode in order to modulate light incident on the optical modulation element based on image data, wherein in the first mode, the optical modulation element is configured to receive the light transmitted and reflected from the optical element and reflect first light rays , as ON light for forming an image based on image data, in a first direction, and in the second mode, the optical modulation element is configured to receive the light transmitted and reflected from the optical element and reflect second light rays , as OFF light not for forming an image, in a second direction different from the first direction, wherein in the first mode, the optical modulation element is configured to receive the light transmitted and reflected from the optical element and reflect first light rays , as ON light for forming an image based on image data, in a first direction, and in the second mode, the optical modulation element is configured to receive the light transmitted and reflected from the optical element and reflect second light rays , as OFF light not for forming an image, in a second direction different from the first direction, wherein the second light rays reflected from the optical modulation element travel on an opposite side of the first light rays reflected from the optical modulation element across the light received by the optical modulation element , the total internal reflection prism unit has an interface (B) that transmits the first light rays to be directed to a projection target for forming the image, and characterised in that the interface (B) reflects the second light rays and the light emitted from the light source to be directed to a position different from the position of the projection target. <EOS>