PURPOSE: To improve the filtration efficiency by double filtration, and also, to make the recovery percentage satisfactory by extending and providing a screen on the peripheral surface of a hollow feed shaft provided with many through-holes, and also, making a mesh of the screen of an outer cylinder and the feed shaft thinner as it goes to the latter half part.

CONSTITUTION: A feed shaft 2 is provided in an outer cylinder in which a screen is extended and provided on the peripheral part, and the feed shaft 2 of a screw press for executing solid-liquid separation by feeding by pressure a raw solution supplied to one end side of the outer cylinder 1 by a spiral blade 3 wound round to its feed axis 2 to the other end side is constituted like a hollow and many through-holes are provided on its peripheral surface. Subsequently, on the peripheral. surface of its feed shaft 2, a screen having minute through-holes is extended and provided, and also, meshes of the screen extended and provided on the outer cylinder 1 and the screen extended and provided on the feed shaft 2 are formed to thin ones from large ones, as they go to the discharge side of cake from the supply side of the raw solution. Accordingly, the filtration efficiency is improved by double filtration, and also, the recovery percentage becomes satisfactory.