PURPOSE: To enable production of a product having no pinholes occuring in generation of gas by subjecting the part of the vibration-damping steel plates to be welded to seam welding, burning and removing the chemical sound absorbing member and subjecting the ends of the steel plates to lap welding then welding the steel plates.

CONSTITUTION: A chemical sound absorbing member 1 such as a plastic material is packed between two sheets of steel plates 2 and 2 to form a sandwich vibration-damping steel plate (a). The member 1 of the part to be welded of such steel plate is burned and removed by seam welding. The steel plate ends of the part where said member is burned and removed are then subjected to lap welding in a hermetic state. Welding such as arc welding, seam welding or the like is performed in accordance with the conventional method by using the steel plates (a), (a) subjected to such end working, by which a product such as an oil pan, oil tank or the like is obtd. The member 1 in the weld zone is prelminarily removed by the above-mentioned method, by which the generation of gas is prevented and the product having excellent airtightness without pinholes is manufactured.