When waiting for printing, a cam that rotates together with the rotation of a gear locks a knurl at position on the upstream side in the sheet conveyance direction, which prevents sheets from dropping down. Moreover, during printing, when the cam is rotated 180° from the locked position, the knurl is in a state capable of sliding toward the downstream side. As a result, with the force that returns the knurl to the upstream side being too small, it is possible to prevent feeding overlapping sheet due to the front end of a sheet further on the down side than a sheet being fed from dropping toward the downstream side further than the knurl.