To prevent double feed of transfer paper sheets by providing a placing plate and a cassette opposite thereto with a connecting means for keeping the placing plate in the depressed state, and setting the release time for the depressing state of the connecting means after the completion of installing a paper feed cassette in an image forming apparatus main body.

When a placing plate 3 is depressed against the forcibility of an elastic body 6, a magnet 7 and a magnetic body 8 are kept in the closely adhering state. When a paper feed cassette 2 is installed in a paper feeder 1 to reach the installation completion position on a guide rail 1A, a detection signal is output from an installation completion detecting means 9 to a control part 11, and in the lapse of designated time, a magnetism generating means 10 is started, so that the placing plate 3 is separated from the magnetic body 8 to bring the placed transfer paper sheets S into contact with a paper feed roller. As the placing plate 3 is pushed up after the completion of installing the paper feed cassette 2, when the cassette reaches the installation completion position in the paper feeder 1, even if impact force is generated, it is possible to prevent the situation where the transfer paper sheet S runs on the upper surface of a corner claw 4.