PURPOSE: To make a display at an indicated position by determining a new position shifted from a position where an underline is stored in an image buffer by an arithmetic processing part and storing the image buffer with a dot image corresponding to the underline at the new position.

CONSTITUTION: A coordinate arithmetic processing part 3 calculates and holds coordinates (X0, X0) of a string of characters of one line and a rectangular range (X0, Y0);(X0+X, Y0-Y)) encircling the characters in a storage device. When a string of characters to be underlined is determined, the leftmost X coordinate Xmin and rightmost coordinate Xmax of a circumscribed rectangle encircling the whole character string and the bottom end Y coordinate of the circumscribed rectangle are calculated in consideration of the circumscribed rectangle. In consideration of the coordinate range (Xmin, Ymin), (Xmax, Ymin) when the characters are underlined in contact with the lower end of the circumscribed rectangle, a value Δ is added to the coordinate Ymin to determine the coordinate rate (Ymin, Ymin-Δ) etc.