To generate a straight line at a high speed by rapidly calculating an initial value.

Data obtained by adding the initial value of a ΔY register 12 by an adder 15 is sequentially supplied to a YA register 13 and stored. Data obtained by sequentially adding the initial value of a ΔX register 10 is stored in an XA register 11. When a value obtained by adding the initial value of the ΔY register 12 to data which is stored in YA register 13 is smaller than data which is stored in the XA register 11, it is cancelled. An XD counter 17 for setting an X-coordinate position in generating the straight line executes counting-up synchronously with an addition processing and the coordinate becomes the X-coordinate in generating the straight line. When the value obtained by adding the initial value of the ΔY register 12 to data which is stored in the YA register 13 is larger than data stored in the XA register 11, a YD counter 18 execute counting-up by synchronism with the addition processing and the coordinate becomes the Y-coordinate in generating the straight line.