A method for producing a high strength workpiece material includes the steps of: placing an alloy material 10 into a central space of a cylindrical mold 2; vertically compressing both end faces of the material in the central space with a press member 5 and a first support member 3, thereby causing one lengthwise end of the material to flow radially outward along an end face of the cylindrical mold 2 to form an expanded part; bringing the press member 5 into contact with a lengthwise end face of the expanded part so as to press the expanded part against the end face of the cylindrical mold 2; and increasing the distance between the press member 5 and the end face of the cylindrical mold 2 while decreasing the distance between the press member 5 and the first support member 3, thereby continuously causing the radially outward flow from one end to another end of the material to gradually increase the thickness of the expanded part.