PURPOSE: To attain shading processing independently of a data form by selecting a data read from a data storage means in response to the data form based on a control means.

CONSTITUTION: A data form signal 6 is inputted to a control means 1 in advance to select a white reference data RAM 2a and a white level reference data 4a is written to an address designated by an address of the signal 6. A black level reference data 4b is written similarly in a black reference data RAM 2b. A line signal 5 is selected as a reset signal 14 of an address counter 12 in the case of a point sequential data and the address is initialized for each line. In the case of a line sequential data, a 3-line signal 13 is selected and the address is initialized for each of 3-line. In the case of an area sequential data, the operation is similar to the case with the point sequential data. When a picture data is inputted, the control means 1 outputs an address 9 in response to the data form and the picture data is corrected.