PURPOSE: To detect whether or not a foreign matter is caught between a top and bottom forces under a low-pressure clamping condition by providing a foreign matter detecting function for low-pressure clamping time by installing an air cylinder to a toggle mechanism section which opens/closes a metallic mold.

CONSTITUTION: An air cylinder 10 is installed to a toggle mechanism section 5 which moves a mobile platen 4 in the vertical direction and, at the same time, clamps a top force 1 to a bottom force 2. While a fair clamping force can be obtained by the mechanism 5 only at the force touching position, the toggle angle θ of the mechanism 5 is increased by the stroke of the cylinder 10. In addition, a foreign matter detecting function is realized for low-pressure clamping time by reducing the thrust of the cylinder 10. Therefore, the foreign matter detecting function which has not been realized at the low-pressure clamping time can be realized by adding the air cylinder 10 to the mechanism 5.