PURPOSE: To provide the titled device which detects also a deposited material having a thickness of not more than 1mm, protects the mold and hardly becomes faulty, by a method wherein an electrical contact element is elastically embedded in one surface at a parting line of the mold, and the other itself is used as one of contacts.

CONSTITUTION: A threaded hole 2 is drilled in the parting line PL of a movable mold 1, and the electrical contact element 3 is screwed into the hole 2 in an embeded manner. The contact element 3 has an electrically insulating cylinder body 4, a spherical body 5 made of steel and a coil spring 6. The rear end of the spring 6 is engaged with a knock pin 9, and a lead wire 11 connected to the spring 6 is connected to the positive side of a power source through an overcurrent-preventing resistor R and a relay 13 for clamping the mold at a high pressure. The negative side of the power source is connected to the fixed-side mold 14. The amount of the part projected beyond the flash line of the mold can be finely adjusted by the spherical body 5, and the material deposited on the mating surface in a thickness of not more than 1mm can also be detected.