PURPOSE: To provide an original discrimination device which can automatically detect the size of an original even in the case when a thick book or the like is set as the original and which prevents the erroneous detection from being executed.

CONSTITUTION: When the detection signal of either an angle detection means 14 or a floating detection means 11 is inputted to a control part 7, original discriminating information inputted from an original discrimination means 6 is decided. For example, in the case of the thin original such as a paper, the opening and closing angle of an original cover plate 9 is detected by the detection means 14 when the plate 9 is closed and the original discriminating information inputted from the discrimination means 6 is decided. In the case of the thick original such as the book, the floating of the plate 9 is detected by the detection means 11 when the plate 9 is closed and the original discriminating information inputted from the discrimination means 6 is decided.