PURPOSE: To achieve the long-term stable operation of a backwashing reproduction type ceramic filter by decreasing filtering speed in the case of a liquid to be treated high in the rising ratio of filtering difference pressure or the lowering ratio of filtering speed per the unit mass of the solid caught by the ceramic filter.

CONSTITUTION: A liquid to be treated is filtered by a ceramic filter 1 and, when filtering difference pressure rises or filtering speed decreases, filtering capacity is restored to again repeat filtering treatment. At this time, in the case of the liquid to be treated high in the rising ratio of filtering difference pressure or the lowering ratio of filtering speed per the unit mass of the solid caught by the filter 1, filtering speed is decreased and, contrarily, in the case of the liquid to be treated low in the rising ratio or the lowering ratio, the filtering speed is increased. For example, when the amount of the solid caught by the filter in the treatment process is 5-100g/m2, the filtering speed is controlled so that the filtering difference pressure rises from the initial difference pressure after the backwashing of the previous time within a range of 1kg/cm2 or less. As a result, the filter 1 can be stably and continuously operated for a long period of time.