An image-data compressing apparatus includes: a start-focus-point setting unit that sets a start-focus point; a draw-point presence/absence setting unit that sets a draw-point presence/absence information bit; a draw-start-point information setting unit that sets a draw-start point information bit; a draw-point-number information setting unit that sets a draw-point number information bit; and a start-focus point/draw-point presence/absence setting unit that sets a draw-point presence/absence information bit, wherein, the respective units repeats the process thereof for a plurality of rows corresponding to the dot columns in the binary image data, to thereby obtain a compressed data of the binary image data from a bit string of the bits set by the respective units.