PURPOSE: To obtain a liquid fertilizer without causing problem in aspects of environmental hygiene at a low cost using a method capable of discharging a treating liquid out of system by passing raw sewage through a treating tank in which a treating agent capable of providing magnetic water is packed.

CONSTITUTION: A treating agent capable of providing magnetic water, e.g. a treating agent obtained by dipping a zeolite, etc., in a liquid obtained by dissolving magnetite, etc., in an acid such as hydrochloric acid and diluting the solution with water and supporting a magnetic material on the treated zeolite is packed in a treating tank. Then raw sewage is passed into the treating tank and organic substance in the raw sewage and Escherichia coli, etc., are removed to provide the aimed liquid fertilizer as the treating liquid. The treating liquid can be discharged by only applying simple treatment thereto when the treating liquid is not used as the liquid fertilizer.