A control device of a head-mounted device is provided. The head-mounted device includes an image capturing device configured to capture an environment around a wearer and a display device configured to display an image to the wearer. The control device includes a first acquisition unit configured to acquire a first image captured by the image capturing device, a second acquisition unit configured to acquire a second image used to lead a mental state of the wearer to a target mental state, and a composition unit configured to composite the first image and the second image, thereby generating a third image to be displayed on the display device.