PURPOSE: To minimize the deformation of a sleeve of a plurality of heat-radiating plates and simultaneously fit with accuracy the plurality of heat-radiating plates on the outer circumference of an oscillation tube, by heating the plates and fixing the same on the oscillation tube by shrinkage force-fitting.

CONSTITUTION: Radiating plates 2 are placed over a mandrel 22 and an oscillation tube 1 is mounted on the mandrel 22. Each support plate 33 of a heat-radiating plate holding jig 30 is inserted between each two adjacent heat-radiating plates. The support plates 33 are heated by a heater 40. After the heat-radiating plates 2 have been sufficiently expanded, the radiating plates 2 are held in place by a pressing jig 15 for heat-radiating plates 2. Then, an oscillation tube 1 is inserted under force into the sleeves of the heat-radiating plates 2 by a press-fitting jig 17. After the heat of the heat-radiating plates are taken away by the environmental air and the oscillation tube 1, the heat-radiating plates 2 are tightly fit on the oscillation tube 1.