In an image forming device, a paper feed cassette accommodating a plurality of papers is removably inserted in a cassette accommodating portion of a device main body. A locking member and a lock releasing member maintain a flapper at a prescribed pressed-down position. When the paper feed cassette is inserted into the cassette accommodating portion, after the flapper at the prescribed pressed-down position is unlocked, the flapper is temporarily caught at a position within a vertical swinging range of the flapper. After the paper feed cassette is completely inserted, the flapper is released.