PURPOSE: To obtain a mark reading rate with high accuracy, by correcting the effect of a card skew at carrying as well as expansion and shrinkage of paper.

CONSTITUTION: A photoelectric conversion signal is stored in a picture memory 2. If a sheet 7 is normally contained in a picture memory 8, the outermost location of each direction can be informed from the projections to both X and Y directions. Thus, a television scanning region to detect coordinates of four end points of a document is set. A coordinate (ax, ay) of B at a point A is scanned toward the X between projections III and III' in Y direction. Then, the change in side of the forms is continuous between them, the document is not jammed and brokened and the position of the end points is normal; those can be confirmed. Simultaneously, the coordinate ax, ay of the end points can be informed.