In performing molding by injecting and filling a resin by an injecting device with a predetermined injection pressure into a mold formed of a fixed mold and a movable mold clamped by a clamping device with a predetermined clamping force, at least a clamping device which enables natural compression of the resin with solidification of the resin in the mold is used as the clamping device, a molding injection pressure and a molding clamping force with which a predetermined mold gap is generated between the movable mold and the fixed mold in injection and filling and a non-defective product can be molded are acquired and set in advance, the clamping device is clamped with the molding clamping force during production, the molding injection pressure is set as a limit pressure, and after the resin is injected and filled in the mold by driving the injecting device.