A mold clamping device includes a frame, a fixed base for supporting a first mold, the fixed base being fixedly mounted on the frame, a movable base for supporting a second mold, the movable base being movably mounted on the frame in confronting relation to the fixed base, first means on the frame for driving the movable base to move rectilinearly toward and away from the fixed base, a cam follower supported on the movable base, a cam supported on the frame and having a cam surface held in contact with the cam follower, and second means for driving the cam in a mold clamping stroke to displace the cam follower for enabling the movable base to clamp the second mold firmly against the first mold on the fixed base, the cam surface being defined by a cam follower displacement curve having a gradient which is greater at an initial stage of the mold clamping stroke and becomes smaller as the mold clamping stroke progresses. When the cam is driven by the second means, the cam follower is displaced thereby to clamp the first and second molds together. The cam is small in size to make the mold clamping device small in size, and is high in rigidity to allow itself to be driven by a small force.