When each of a plurality of projection devices projects an image on a screen, in order to easily determine whether or not an association between identification information of each of the plurality of projection devices and positional relationship of each of the plurality of projection devices is correct, an image for notifying of an association between a predetermined area included in a display pattern and an external projection device is projected, and a communication unit of a projection device transmits information related to the association between the predetermined area included in the display pattern and the external projection device, which is inputted by an input unit, to the external projection device.