To determine a paper type without using a special sensor for determining the paper type.

This paper type determination device is provided with: a paper type determining sheet carrying passage SH2 used for carrying a sheet S for recording an image thereon, and formed to extend a carrying time of the sheet S with low stiffness relative to that of the sheet S with high stiffness; a sheet carrying device SH1+SH2+Ra+Rr carrying the sheet S to the paper type determining sheet carrying passage SH2; sheet sensors SN1 and SN2 detecting the sheet S to be carried through the paper type determining sheet carrying passage SH2; a sheet carrying time measurement means C6 measuring a sheet carrying time TMa until the sheet S carried through the paper type determining sheet carrying passage SH2 is detected by the sheet sensor SN2; and a paper type determination means C8 determining the paper type of the sheet S from the sheet carrying time TMa measured by the sheet carrying time measurement means C6. This image forming device is equipped with the paper type determination device.