In a smartphone, the imaging mode of an imager or the display mode of a display is changed from a normal mode when an image of an optical communication region is captured. More specifically, a process of lowering the contrast of the entire image (frame), a process of superimposing an icon image on the candidate region, a masking process for lowering the contrast of the candidate region, a process of reducing the count of display frames by image averaging or thinning, or a zoom limiting process of limiting the upper limit of the zoom ratio of the imager or the upper limit of the enlarged display magnification on the display is performed.