An image projection apparatus, comprising: an optical image generating unit to generate an optical image based on image data; a projection optical system including a plurality of optical elements and configured to project an image onto a projection surface, the projection surface not forming part of the image projection apparatus, the projected image being coupled with the optical image generated by the optical image generating unit wherein the projection optical system includes a first optical system and a concave surface mirror, the first optical system configured to generate an intermediate optical image coupled with the optical image generated by the optical image generating unit, the concave surface mirror configured to project an image coupled with the intermediate optical image onto the projection surface; a projected image shifting unit (41, 42) to shift the projected image by changing a posture of at least one of the plurality of optical elements included in the projection optical system; a tilt sensor to detect a posture of the optical element of which posture is changed by the projected image shifting unit (41, 42); and a trapezoidal distortion correction unit (53, 53b) to correct the optical image generated by the optical image generating unit so as to prevent the trapezoidal distortion of the projected image from occurring based on the detection result of the tilt sensor; characterized in that the optical element of which posture is changed is the concave surface mirror, and the shifting unit (41, 42) is configured to change the posture by tilting and shifting the concave surface mirror in a direction corresponding to a vertical direction when the image projection apparatus is oriented for normal use. an optical image generating unit to generate an optical image based on image data; a projection optical system including a plurality of optical elements and configured to project an image onto a projection surface, the projection surface not forming part of the image projection apparatus, the projected image being coupled with the optical image generated by the optical image generating unit wherein the projection optical system includes a first optical system and a concave surface mirror, the first optical system configured to generate an intermediate optical image coupled with the optical image generated by the optical image generating unit, the concave surface mirror configured to project an image coupled with the intermediate optical image onto the projection surface; a projected image shifting unit (41, 42) to shift the projected image by changing a posture of at least one of the plurality of optical elements included in the projection optical system; a tilt sensor to detect a posture of the optical element of which posture is changed by the projected image shifting unit (41, 42); and a trapezoidal distortion correction unit (53, 53b) to correct the optical image generated by the optical image generating unit so as to prevent the trapezoidal distortion of the projected image from occurring based on the detection result of the tilt sensor; characterized in that the optical element of which posture is changed is the concave surface mirror, and the shifting unit (41, 42) is configured to change the posture by tilting and shifting the concave surface mirror in a direction corresponding to a vertical direction when the image projection apparatus is oriented for normal use.