According to the present invention, a reduction printing apparatus includes: an n-line memory unit (1) for storing an object line "n" to be thinned-out in binary images extended on a bit map;an n-1/n+1-line memory unit (2) for storing the first line "n-1" before the object line "n", or the first line "n+1" after the object line "n", an n-2/n+2-line memory unit (3) for storing the second line "n-21" before the object line "n" or the second line "n+2" after the object line "n"; an output means (1,2,4) for performing an OR logic process between the n-line memory unit (1) and the n-1/n+1-line memory unit (2), and outputting the result to an A-line memory (6); an output means (1,2,5) for performing an AND logic process between the n-line memory unit (1) and the n-1/n+1-line memory unit (2), and outputting the result to a B-line memory (7); and a 2-1-selector (8) selects either the A-line memory (6) or the B-line memory (7) in accordance with the content of the n-2/n+2-line memory unit (3), and outputs the result to a C-line memory (9); wherein when the content of the n=2/n+2-line memory unit (3) is the column for "0", the 2-1-selector (8) selects the content of the A-line memory (6), and when the content of the n-2/n+2-line memory unit (3) is the column for "1", the 2-1-selector (8) selects the content of the B-line memory (7), and the selected contents are output to the C-line memory (9) for printing.