The pattern data generating unit generates pattern data indicative of a pattern of a plurality of marks including a plurality of first marks each having a first color and a plurality of second marks each having a second color so that a first target-total is equal to a second target-total. The first target-total is a total of deviations of first target-positions from a reference position in a predetermined direction. The second target-total is a total of deviations of second target-positions from the reference position in the predetermined direction. The controlling unit controls the image-forming unit to calibrate the second target-positions based on the offset of a second actual-total from a first actual-total.