In a projector, a comparator included in a trapezoid correction unit compares the aspect ratio of a rectangular input unit with that of the device area. A projection area determination unit determines an effective projection area that is an area included in the projection area and that is rectangular on the object on the basis of a result of the comparison. The device area determination unit determines an effective device area so that the relation of the effective projection area with the projection area corresponds to the relation of the effective device area with the device area. A geometric transformation unit projects the input image into the effective device area so that the input image is projected without distortion within the effective projection area of the object.