PURPOSE: To make a die thin in thickness, light in weight and low in cost by fixing the periphery of the die with cushioning material larger in linear expansion coefficient than a die case.

CONSTITUTION: The cushioning material 3 between the outer periphery of each die body 1 and the die case 2 is formed by material large in linear expansion coefficient thickly in the circumferential direction of a die case 2. The cushioning material 3 is of copper alloy having a linear expansion coefficient 12-30×10-6/°C. Further, the cushioning material 3 has an elliptical outer periphery and forms a doughnut-shaped shrinkage fitted part 3a to fix the die body 1 in the central part and when the cushioning material 3 is raised up to the extrusion temperature in an extruding time, the inside diameter 3a is set to be nearly the same dimension as the outside diameter of the die body 1. In this way, the ununiform compression stress acting on the die body 1 is dispersed to prevent the die from cracking and breaking.