To provide an original reader which is reduced in labor and time for periodically changing reference data used for black and white judgment.

The black and white judgment to image data of a read original is performed based on the reference data read from a reference data storage part 62 assigned to a memory. A character string for abnormality detection preliminarily stored in the memory is discriminated by a character string discrimination part 73, when an abnormal state detection part 74 detects an abnormal state of the memory based on its discrimination result, reference data is generated by reading a white reference board by a scanner 2 and the reference data is stored in the reference data storage part 62. Thus, since the reference data is automatically changed when the abnormal state of the memory is detected, the time for periodically changing the reference data is reduced.