PURPOSE: To provide a filter being capable of exchanging and reusing a screen without stopping an operation by extending a screen formed by closely laminating a plurality of stainless steel wire nets of fine mesh within a filter chamber.

CONSTITUTION: An expanded filter chamber 4 is formed on the way of a duct 2 and a screen 5 formed by piling plural fine mesh stainless steel net 6 is inserted through a slit 4a, 4b formed at about center portion of the chamber 4 and maintained under tension between winding rolls 7 and 8. In front of a winding position of the winding roll 8 at an upper portion of a receiving case 17, a brush 21 for brushing each screen 5 is supported by a shaft in a freely rotating manner and a drawing type drain box 23 is inlaid below the case 17 in a freely slidable manner.