PURPOSE: To apply proper gradation correction to a color picture by using the read values of a color chart and a prescribed pattern.

CONSTITUTION: In the case of executing automatic gradation correction, a CPU 313 allows a reader part 301 to read out a color chart and a test pattern and finds out a correction value to be set up in a printer gradation correcting circuit 316 by operation based upon the read results. In the case of correcting a C color component e.g. input masking processing is turned off, R, G and B values obtained by reading out the C color part of the color chart are respectively set up as Rco, Gco, Bco and R, G and B values obtained by reading out the C color part with density Di of the test pattern are set up as Rci, Gci, Bci. Density is measured based upon an R signal, and when a C color component signal with density Dci is inputted, the contents of a table in the circuit 316 are changed so that the C color component signal with a prescribed value is outputted to correct the gradation of a printer part.