To provide a copying device capable of improving the conveying performance of a long document and the like, and simplifying the operation performed by a user.

When a tip of a document enters into an inlet sensor, the prefeed of the document is started. A thickness of the document is checked at a time when the tip of the document is inserted into a feed roller. The thickness of the document is transferred into voltage by a PSD sensor to be outputted, then the voltage is inputted to an A/D port, and the thickness of the document is calculated on the basis of the predetermined table data. Then a stepping motor is driven by the thickness on the basis of the calculated thickness. A position of a document face is set on a constant position even when the thickness of the document is changed.