The present specific document determining apparatus according to the present invention comprises a microwave sensor for irradiating a microwave to and scanning a document, detecting a reflected portion of the irradiated microwave, outputting a first detection signal, again irradiating a microwave and scanning the document after the document is placed on a contact glass, detecting a reflected portion of the irradiated microwave, and outputting a second detection signal; a signal processing section for using the first detection signal as a reference signal and comparing a level of the reference signal to a level of the second detection signal to make determination as to whether metallic fiber is included in the document or not, and a controller for making determination as to whether the document is a specific one or not according to a result of determination by the signal processing section.