An image processing device performs image processing on image data for projection into a projection area. The image processing device comprises a memory and an image processor. The memory at least temporarily stores image data. The image processor specifies a certain area that is part of the projection area and extends from one end of the projection area, and corrects the image data so as to satisfy a certain condition on the basis of the specification of the certain area. The certain condition is that the correction amount A for the brightness of the image data portion to be projected into the certain area and the correction amount B for the brightness of the other image data portion in the projection area satisfy the relation A