surface of the photosensitive drum 3 as the photosensitive drum 3 in the process cartridge 10 is rotated the peripheral surface of the photosensitive drum 3 is uniformly charged by the charging device 4 of the roller type then an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 3 by the beam of laser light projected upon the peripheral surface of the photosensitive drum 3 by the scanner unit 2 then the electrostatic latent image is developed by the developing apparatus 5 the latent image is supplied with toner by the developing apparatus 5 whereby a visible image which reflects the latent image is formed of the toner on the peripheral surface of the photosensitive drum 3 there are multiple sheets 12 of a recording medium in a sheet feeder cassette 11 the sheets are stored in layers in the cassette 11 the sheets 12 of the recording medium are sheets of paper for example and are roughly 64 216 g in basis weight each sheet 12 of the recording medium in the cassette 11 is fed into the main assembly of the image forming apparatus by a feed roller 13 while being separated one by one from the rest by the feed roller 13 after.