A mold clamping apparatus of the type including a mold opening/closing actuator and a mold clamping cylinder, wherein rails for guiding a movable platen are disposed on a base, and the mold clamping cylinder has a left leg and a right leg each disposed between one pair of left and right rails of the rails. The rails provided for guiding the movable platen is used also as a side guide for the mold clamping cylinder. This arrangement can obviate the need for a separate guide member.