PURPOSE:To make initial setting operation at a home position easy by a method wherein a distance to a density-measuring start reference position from the home position as a start point is corrected by a drift quantity to obtain a corrected distance, and a position separated by this corrected distance is taken as the density-measuring start reference position, CONSTITUTION:Density of a reference mark 100-1 is fetched to a host computer part 9 accompanying transfer of a density-measuring head. Then, said host computer part obtains a central position of the reference mark 100-1 from the fetched density value by performing specific operation, and a shift quantity LC between a distance LB from a provisional home position 111 to the central position of the reference mark 100-1 and a distance LA from a home position H0 to the central position of the reference LC is substrated from a distance LD from the home position H0 as a start point to the predetermined density measuring start reference position to obtain a correction distance LE. A position separated by this correction distance LE is taken as the density measuring start reference position from the temporary home position H1.
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