1. A vehicular instrument display device comprising: a display panel for displaying an instrument image including an index image constituting an index and a pointer image constituting a pointer for pointing the index; and a controller for displaying the instrument image on the display panel, wherein the controller varies at least one of a pointer display mode and an index display mode so as to increase readability of the index indicated by the index image when positions associated with the index image and the pointer image coincide; and wherein the controller varies the index display mode such that a plurality of supplementary images are displayed on a periphery of the index image so as to increase readability of the index indicated by the index image; and the controller displays each said supplementary image with a central brightness and hue between a brightness and hue of the pointer image and a brightness and hue of a background of said instrument image; and the controller displays said index image and pointer image with the same brightness and hue when said pointer image coincides with said index image; and wherein the plurality of supplementary images are added to only one side of each of one or more boundaries of said index image and wherein said index image is not fully enclosed by said boundaries when said pointer image coincides with said index image.