To provide: an image forming device capable of displaying a display screen at high speed; a display device; a screen display method; and a screen display program.

The image forming device 100 including a display device 21 comprises: a retention means 41 for retaining a first image 52 composed of a first image area 52b having an opaque parameter value as the transparency parameter showing the transparency of a pixel and a second image area 52a having a translucent parameter value; and a composition means 42 for superimposing and composing the first image 52 retained by the retention means 41 over a second image 51b displayed on the display device 21.