In a mold clamping apparatus, a mold clamping mechanism is provided with a half nut, and a tie bar is provided with circumferential groove configured to meshed with the teeth of the half nut. A strong-force mold opening mechanism that opens molds at an initial stage of mold opening extends across a space separating a movable platen and the mold clamping mechanism and is connected to the movable platen and the mold clamping mechanism. The strong-force mold opening mechanism is set so as to have greater axial force and shorter stroke than those of a mold opening and closing mechanism. A control unit controls opening and closing of the half nut, controls the strong-force mold opening mechanism and controls the position of the half nut in such a way that the half nut is synchronized with the circumferential groove by the strong-force mold opening mechanism.