A smoothing belt (27, 127, 127A) adapted to be disposed in a smoothing press apparatus (100, 200), for smoothing a surface of a wet paper web by being pressed, together with the wet paper web, by a pair of press rolls (23, 25), said smoothing belt (27, 127, 127A) comprising: a base body; a first batt layer disposed on a wet paper web side surface of said base body; a second batt layer disposed on a roll side surface of said base body; and a porous thin film layer, disposed on a wet paper web side surface of said first batt layer, for direct contact with said wet paper web, wherein said porous thin film layer is a foamed resin layer being applied in an amount ranging from 50 g/m 2 to 150 g/m 2, characterized in that the foamed resin layer is formed by mixing a polyurethane resin, a plurality of types of surfactants having different hydrophilic degrees, and a powder of inorganic compound with a solvent to form a mixture, and impregnating said first batt layer from said wet paper web side surface with said mixture to form an impregnated layer, said mixture being also put on said first batt layer, said first batt layer being then held in contact with water to extract said solvent and said powder of inorganic compound to convert said impregnated layer into a porous foamed resin layer, wherein said smoothing belt (27, 127, 127A) has an air permeability ranging from 1 cm 3 /cm 2 /sec to 5 cm 3 /cm 2 /sec, and wherein pore diameters in a certain range are obtained by using together hydrophilic surfactants with high HLB (Hydrophile Lyophile Balance) values and lyophilic surfactants with low HLB values, the diameters of the pores of the foamed resin layer being held to a range from 20 μm to 100 μm by using the plurality of types of surfactants. a base body; a first batt layer disposed on a wet paper web side surface of said base body; a second batt layer disposed on a roll side surface of said base body; and a porous thin film layer, disposed on a wet paper web side surface of said first batt layer, for direct contact with said wet paper web, wherein said porous thin film layer is a foamed resin layer being applied in an amount ranging from 50 g/m 2 to 150 g/m 2, characterized in that the foamed resin layer is formed by mixing a polyurethane resin, a plurality of types of surfactants having different hydrophilic degrees, and a powder of inorganic compound with a solvent to form a mixture, and impregnating said first batt layer from said wet paper web side surface with said mixture to form an impregnated layer, said mixture being also put on said first batt layer, said first batt layer being then held in contact with water to extract said solvent and said powder of inorganic compound to convert said impregnated layer into a porous foamed resin layer, wherein said smoothing belt (27, 127, 127A) has an air permeability ranging from 1 cm 3 /cm 2 /sec to 5 cm 3 /cm 2 /sec, and wherein pore diameters in a certain range are obtained by using together hydrophilic surfactants with high HLB (Hydrophile Lyophile Balance) values and lyophilic surfactants with low HLB values, the diameters of the pores of the foamed resin layer being held to a range from 20 μm to 100 μm by using the plurality of types of surfactants.