The invention provides a method for setting a clamping force of an injection mold and a clamping force setting apparatus. The method comprises the steps of closing a metal die according to a set clamping force, injecting melted resin inside the metal die through an injection mechanism, setting a required minimum clamping force required for the metal die during a closed state, and calculating maximum increase of clamping force of the mold, which is the difference between the generated clamping force of the injection mold when the injection mold closes and a maximum clamping force of the injection mold during the injection molding process. Then, a transition point from a region of maximum increase of the clamping force of the injection mold is determined, and the predetermined clamping force of the injection mold is reduced to another region in which the clamping force is increased to a higher rate. The immediate transition of clamping force from one state to another state is carried out, for determining the required minimum clamping force of injection mold in which the injection mold does not open.