In a mold clamping device including a fixed platen, a movable platen, a plurality of tie bars, and mold clamping half nuts, a pair of additional half members which is restricted in the axial direction of the tie bar and moves in an opening/closing direction of the half nuts relative to the mold clamping half nuts is further provided, and when the mold clamping half nuts are closed and mated with the screw or the ring groove of the tie bar, the additional half members are closed to hold the tie bar so that play at mated parts is removed or cancelled by fixation.