To provide an image reader which reads a plurality of originals on an original placing table to generate read image data for each original, the image reader reading the respective originals in different operation modes and efficiently reading them.

The image reader sets, when a main scanning instruction is input, the lowest reading resolution among reading resolution set to the respective originals as reading resolution for light intensity adjustment based on the operation modes of the respective originals placed on the original placing table (S330). Then, the image reader causes a line sensor to read a white reference member with the reading resolution, and specifies a proper value L0 of the light quantity used when the originals are read with the reading resolution, based on reading results of the white reference member (S340). Furthermore, on the basis of the proper value L0, the image reader calculates a proper value LM of light quantity to be output from a light source in original reading with the read resolution set to the respective original (S360). Thus, after setting original reading characteristics corresponding to the operation modes set to the respective originals, scanning of the respective originals is started (S390-S495).

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