In a mobile terminal apparatus, a display unit displays a diagnostic image read from an image storage device. The image storage device stores plural image groups, each of which includes plural diagnostic images. Movement of the display unit is detected. Assuming that the display unit is moved in a mode of transverse movement while a first diagnostic image included in a first image group is displayed on the display unit, then changeover is carried out to display a second diagnostic image being included in the first image group and different from the first diagnostic image. Assuming that the display unit is moved in a mode of a single shake different from the mode of transverse movement while the first diagnostic image is displayed on the display unit, then changeover is carried out to display a third diagnostic image being included in an image group different from the first image group.