This paper proposes a force magnifying mechanism for a parallel jaw gripper that can exert a large grasp force. A parallel jaw gripper requires speed when opening and closing its jaws, and force when grasping an object. The proposed force magnifying mechanism consists of a slider, feed screws, gears, a lever, etc. It runs sequentially with only one DC-motor. Basically the motor rotates a feed screw to move its output jaw quickly to an object with a gear. When the output jaw makes contact with an object, the gear is loosened from a stopper and starts to move axially along the feed screw. Then it pushes a lever, which generates a large fingertip force. We have developed an 86g gripper with this mechanism and experimentally verified that it can grasp objects of various sizes with a large grasp force over 200N. It is also experimentally verified that the gripper can grasp and ungrasp an object reliably over 4500 times if machine lubricant is properly supplied.