To perform a return processing of an abnormal form at high speed by detecting type of an inserted form such as a call letter, a passbook and their propriety immediately after insertion.

This form processor is provided with a width detection mechanism 2, a thickness detection mechanism 5 and a magnetic stripe detection mechanism 6 and discrimination of the type and the propriety of the inserted form is performed from three viewpoints such as the width, the length and presence/absence of magnetic stripes of the form. In addition, the type of the form in short time from the insertion by executing detection of the width, the thickness and presence/absence of magnetic stripes during fetching period of the form. Thus, the time for switching various conditions and environment in a unit is secured according to the kind of the form discriminated by them and the return processing of the abnormal form is performed at an early stage.