In at least one embodiment of the disclosure, a projector comprises an imaging unit that photographs a projection surface and acquires a first photographed image during a projection of a featured image at a first time point and acquires a second photographed image during the projection of the featured image at a second time point different from the first time point. An image processing unit generates a reference image based on the first photographed image and generates a comparative image based on the second photographed image. A movement detecting unit detects a change in a relative position of the projector with respect to the projection surface by using the reference image and the comparative image generated by the image processing unit.