PURPOSE: To facilitate an operation for finding out what part of display an effect in the case of changing a variable density level appeares at in a display device in which multicolor display data is expressed with the variable density of monochrome.

CONSTITUTION: What key is depressed among 16 color specifying keys 1 for specifying 16 colors is judged by an input key identification part 2, and a changing processing part 4 rewrites corresponding information between color and variable density based on the judged result and the content of the change of the variable density outputted from a changing designating means 3.