To predict, on a computer, rapture of a spot welding part in a structural member for an automobile, in details, when deformed by collision, as to spot welding for the member.

This device for predicting the rapture of a spot welding part has an input means for inputting material strength, a plate thickness, a nugget diameter of the spot welding, a plate thickness of a joint, and a rotation angle of the joint in a tension test, on a basis of a cross type tension test and/or shearing type tension test, in a spot welding joint, a computing means for calculating a rapture strength parameter of the spot welding part, from the material strength, the plate thickness, the nugget diameter of the spot welding, the plate thickness of the joint, and the rotation angle of the joint in the tension test, a parameter storage means for storing the rapture strength parameter in every steel kind, and a computing means for introducing the rapture strength parameter stored in the parameter storage means into a rapture prediction expression modeled with deformation in the periphery of the spot welding by a finite element method to determine the rapture of the spot welding part.