A character attribute determination section 1 determines a attribute of a character on the basis of a character attribute database 2. A blur intensity decision section 5 acquires a blur intensity for each character attribute on the basis of legibility control knowledge 3, and decides the blur intensity for the target character corresponding to the character attribute determined by the character attribute determination section 1. A blurring process execution section 6 performs a blurring process to the character with the blur intensity decided by the blur intensity decision section 5.