To provide an inexpensive single-path color printer capable of precisely aligning a color plane image.

A controller 60 controlling the alignment of a sub image is provided with a CPU 62 communicating with a printing engine 10 and a RAM 66 and a ROM 68. A color plane raster buffer 70 stores a printed image as the color plane image of each color. An alignment mark procedure 76 cyclically prints an alignment mark on a medium carrying belt. An alignment mark calculation means 78 calculates an adjusting parameter from the timing and the error of the alignment mark detected, and stores it in an image plane adjusting parameter area 80. By using the adjusting parameter, a buffer control procedure 72 changes the supply of image data to the printing engine 10 from the buffer 70 so as to correct the offset, the asymmetry or the fluctuation of width of the color plane image detected.