PURPOSE: To make a web uniformly wet and to form a homogeneous paper web by adjusting water level in suction boxes arranged to face each other in a sieve circuit to keep a sieve under water surface.

CONSTITUTION: In a double sieve former, in the sieve circuit of a first sieve 1 and a second sieve 2, a first suction box 4, in which a plurality of dewatering bars 5 are elastically arranged by being away, and a second suction box 14, in which a plurality of dewatering bars 15 are inelastically arranged by being away, are arranged to face each other above and below with at least partial overlap. Further a vacuum section is joined to both suction boxes 4, 14 via a vertical tube, fluid level in the vertical tube is made to be adjustable, a dewatering path which is horizontal or vertical or inclined with some angle to a horizon is provided spreadingly and the both sieves 1, 2 are kept under the water level by sieve water in respectively corresponding suction boxes 4, 14. Thus the passing paper web is always made to be uniformly wet.