Moreover in this example, there is no problem such as damage to the gears and so forth caused by food bumping into them, since the right frame 2b covers the drive shaft 19, the drive gear 20, the rolling gear 9 and the flat gear 5, while the sliding members 3 are covered by the flanges 2e provided on the upper left and right parts of the frames 2a and 2b, the gear shaft 4 is covered by the rear fr