PURPOSE: To obtain a reduced picture with fidelity to an original picture by deciding a conversion picture element based on a logic arithmetic operation of coefficients corresponding to a position in the vicinity of the prescribed number of original picture elements whose conversion processing is already finished when data representing exceptional processing are entered.

CONSTITUTION: The picture reduction device is provided with a conversion table 17 storing data representing prescribed conversion picture elements and data representing exceptional processing and a conversion processing section 16 counting line segments in the main scanning direction and the subscanning direction resident in an area of the prescribed number of original picture elements and inputting data from the table 17. Then the processing section 16 stores tentatively the result of count to a main scanning line buffer 11 and a subscanning line buffer 12 and receives data representing the exceptional processing to start an exceptional conversion processing section 10. The processing section 10 decides the conversion picture elements based on the number of the line segments stored in the buffers 11, 12 and picture elements which is already in existence in the vicinity of the current conversion picture elements and whose value is already decided and stored in a line buffer 15. Thus, the reduced picture with fidelity to the original picture is obtained.