PURPOSE: To reproduce an output color picture signal as a 2nd signal from an input color picture signal as a 1st signal with excellent accuracy without causing increase in the entire hardware and the hardware cost.

CONSTITUTION: In order to give a reproduction characteristic with fidelity between input picture signals such as color picture density signals DB, DG, DR and output color picture signals such as color density signals DY, DM, DC, the color picture signal conversion system is realized, which is provided with a color signal conversion circuit 3A based on the projection conversion method in which the relation of function between the both is expressed in equation 1.