To adequately remove fine particles without using flocculating agents by spreading one or multiple sheet-like treating films contg. magnetic objects and conductive objects in raw water and energizing these sheets with DC currents.

The one or multiple sheet-like treating films 1 contg. the magnetic objects or conductive objects are spread in the raw water and are energized with the DC currents. In the case such treating films 1 are used at a dredging work site, the treating films 1 are used by a method for completely enclosing the dredging work site with the treating films 1 or the dredging work area is enclosed by successively joining the rectangular strip-shaped treating films 1 by using floats, etc., by disposing spacings between the adjacent treating films 1 or the treating films are spread to a linear shape or various shapes. As a result, the fine particles are adequately removed without using the flocculating agents.