PURPOSE: To eliminate the difference of read output in FB (flat bet) and that in ADF (automatic paper feeding) in a picture reader which executes reading in FB and that is ADF.

CONSTITUTION: A reference original is read in FB and the output of an A/D converter 16 at that time is stored. The same reference original is read by ADF and the value of a reference white level signal inputted to the A/D converter 16 is changed so that read output at that time becomes equal to read output at FB so as to store the change rate α of the reference white level signal when they become equal is stored. The value of the reference white level signal inputted to the A/D converter 16 is set to be α times as much as the reference white level signal inputted to the A/D converter at the time of regular reading in FB.