A mold clamping device includes a fixed platen on which a fixed mold is disposed, a movable platen on which a movable mold that defines a cavity along with the fixed mold is disposed, a tie bar configured to resist a mold clamping force that is generated between the fixed platen and the movable platen, and a half nut opening and closing device configured to grip the tie bar, thereby locking the movable platen and the tie bar, in which the half nut opening and closing device includes half nuts configured to grip the tie bars, an actuator which is disposed on the movable platen and configured to move the half nuts back and forth with respect to the tie bars, and a clevis configured to connect the actuator to the half nuts so as to allow the actuator to swing with respect to the gripping member.