The projector executes a detection step of detecting a rotational angle of the projector with respect to a horizontal direction, a determination step of determining a correction parameter of correcting a shape of an image to be projected based on the rotational angle detected, a correction step of correcting the shape of the image based on the correction amount determined in the determination step, and a projection step of projecting the image corrected in the correction step. In the determination step, a range of the installation angle at which the projector is installed is divided into a plurality of areas, which of the areas the rotational angle detected in the detection step belongs to is determined, and the correction parameter is determined based on a difference between the reference angle set in the area to which the rotational angle is determined to belong and the rotational angle detected.