To prevent clogging of a strainer of a support plate for supporting a catalytic bed by arranging an air sending means for blowing air in under a support plate installed in a multiple manner in the contacting column in the process in which raw water is contacted with adsorbing particles in a contacting column to adsorb suspended solid in raw water before the treated water is taken out.

When raw water fed to the bottom of a contacting column from a raw water feeding pipe 14 flows upward in the column through strainers 12 of multiple support parts 11 in the up-and-down direction, it is contacted with adsorptive particles of a contact bed 13 on a support plate 11 of each stage to adsorb and remove SS, and the treated water is taken out from the upper end part in the column to outside the column through a water collecting pipe 16. In washing, first after the supply of raw water to the contacting column is stopped, until the level in the column reaches a broken line 17, the water is drained from a drainpipe 20. Next, pressurized air from an air source is jetted from an air feeding pipe 18. In this way, waste fiber and SS are removed and SS struck on the adsorptive particles is removed. After that, the raw water is caused to flow upward in the column and overflows into an overflow weir 15 together with the floated waste fiber and SS and is discharged from a takeoff pipe 19.