a transfer unit that transfers an image-formed medium by rotation thereof;

an image-forming unit that includes a first ink head and a second ink head arranged in a transfer direction of the image-formed medium at a predetermined interval and controls the first and second ink heads to eject first and second inks on the image-formed medium;

a transfer amount detecting unit that outputs a pulse signal in response to a rotational motion of the transfer unit;

a transfer reference position detecting unit that detects a reference position provided on the transfer unit;

an ink landing position calculating unit that calculates an ink landing position corresponding to the reference position on the image-formed medium by counting a pulse signal after detection of the reference position;

a storage unit that stores correction values for printing timing for one rotational cycle of the transfer unit as a correction table; and

a printing timing signal generating unit that reads out a correction value for printing timing, which corresponds to the ink landing position on the image-formed medium, from the correction table and generates a printing timing signal by shifting a phase of the pulse signal by the correction value for printing timing;

wherein the correction table includes a set of values, each value being calculated based on a measurement value of an interval between a first ink landing position by the first ink head and a second ink landing position by the second ink head in a predetermined image pattern formed on the predetermined image-formed media which are corresponding to a length longer than the one rotational cycle of the transfer unit, and canceling an error of a transfer amount of the predetermined image-formed media by the transfer unit, and

wherein the image-forming unit forms an image on the image-formed medium in transfer by controlling the first and second ink heads to eject the first and second inks in synchronization with the printing timing signal.