To eliminate blur from a boundary by detecting a color boundary pixel from an image data, performing printing in main scanning direction while masking the even pixels in odd rows or the odd pixels in even rows and then performing printing of masked pixels by moving a head in the reverse direction.

A color boundary pixel is detected at a color boundary detecting section 2 and recorded at a color boundary recording section 3. A head 8 is provided with n ink ejection heads in the subscanning direction (y) and each pixel is printed by moving the ink ejection heads in main scanning direction through a carriage motor 7 while ejecting yellow, magenta, cyan or black ink from the ink ejection heads. A mask pattern recording section 4 records a pattern for masking the even pixels in odd rows and the odd pixels in even rows having the number of ink ejection heads n of the head 8 in the subscanning direction (y) and the number of pixels of an image to be printed in the the y direction.