PURPOSE: To attain reading without causing a distortion resulting from reduction due to a tilt by obtaining an optimum feeding distance based on a feeding distance being a reference for a read head from dissociation and the tilt of an original face based on the dissociation.

CONSTITUTION: Prescanning is implemented to obtain a dissociation data of an original face 12a prior to the scanning for reading an original, and a dissociation detection means 24 measures a dissociation from a reference face 11a up to the original face 12a at points Pn-3-Pn+1 and the dissociation is inputted to an arithmetic circuit 28 together with data of the points Pn-3-Pn+1 and stored in a memory 29. Then read scanning is implemented to read the original face 12a. At the read scan, the read head 13 starts reading, an optimum step feed distance corrected by a tilt angle θ of the original face 12a stored in the memory 29 is used based on a reference step feed distance l for the step feed distance for the read points Pn-3-Pn+1.