PURPOSE: To improve readout precision by measuring the skew extent of character lines easily and securely even when the reference side of a slip is defective, and correcting its inclination.

CONSTITUTION: A buffer 13 stores a picture signal I from a photoelectric conversion part 10 temporarily according to an X address supplied from an X address counter 14. Then when the image signal I is stored in the buffer 13, a block projection memory 15 stores a horizontal projection. Further, a control part 18 calculates the skew extent of character lines on the slip 12 on the basis of the horizontal projection outputted from the block projection memory 15. A coordinate converting circuit 19 performs coordinate axis conversion for the picture signal I in the buffer 13 on the basis of the information on the skew extent supplied from a control part 18 and respective addresses from X and Y address counters 14 and 16.