An image generating apparatus 10 acquires information associated with a motion of a head of a user wearing a head-mounted display 100. For a period of time for which the head is stopped, the image generating apparatus 10 generates a display image 70 with a standard resolution, and transmits the display image 70 to the head-mounted display 100, so that display images 71 having the same resolution are displayed. For a period of time for which the head is moved, the image generating apparatus 10 generates display images 72 each having the reduced resolution, and the head-mounted display 100 generates display images 73 obtained by enlarging the display images 72.