To display an image even on a projection surface having complex unevenness similarly to a flat, a projection device includes: a storage unit storing at least a pattern image for detecting distortion depending on a state of the surface, an expected image associated with a displayed image of the pattern image displayed on a flat, and a desired projection image; a projection unit projecting an image including the pattern image and the desired projection image; an image acquisition unit acquiring a displayed image of the pattern image, and extracting a distortion image; a distortion amount calculating unit calculating a distortion parameter for distortion by comparing the expected image with the distortion image; a distortion correction processing unit correcting the projected desired projection image by using the distortion parameter; and an image output unit outputting, to the projection unit, image data including the corrected desired projection image and the pattern image.