PURPOSE: To reduce the cost of a color multivalued image printing system by developing bit map data in a page memory capable of storing for 1 screen and forming an image on a given medium in accordance with the bit map data to be developed.

CONSTITUTION: In a color printer 10, a control circuit 12 for controlling the whole and a command analyzing circuit 14 for analyzing print command from a host computer 30 are provided. A page memory 16 for storing multivalued bit map data of 1 color to be printed for 1 screen and a developing circuit 18 for developing printing data from the host computer 30 into multivalued bit map are provided. An image forming device 20 for forming images on a printing paper in accordance with the bit map data on the page memory 16 is provided. Also, an operation panel 22 for designating the operation of the color printer 10 and an interface 24 for connecting the host computer 30 are provided.