To make it possible to shape a filter fiber sheet with a high dimensional accuracy by stacking a fiber sheet for a filtering medium on the surface of a base mold with plural recessed parts and sequentially arranging a force in each of the recessed parts of the base mold, and fixing an uneven pattern on the fiber sheet by heating both base mold and forces at molding temperatures.

First a fiber sheet 4 is stacked on a base mold 2 with mold grooves and a force 5 is sequentially arranged in each of the mold grooves from above the fiber sheet 4. Next, the forces 5 and the base mold 2 are clamped with a clamping tool 6 and fixed under a clamping state. Further, the fiber sheet 4, embossed to the uneven pattern formed along the surface shape of the forces 5, is brought into a gas oven together with the base mold 2 and the forces 5 in such a state that the fiber sheet 4 is embossed. Then the sheet 4 is heated at molding temperatures for a specified molding time, and after being left along for cooling, the clamping tool 6, the base mold 2 and the forces 5 are removed and the filter fiber sheet 9 with long-lasting self- shape retaining properties and sheet grooves 10 fashioned after the surface shape of the base mold 2 and the force 5, is completed.