PURPOSE: To prevent thickening in both end parts of seamless metallic tube which is obtained by rolling an extruded tube for reducing its outer diameter with a stretch reducer.

CONSTITUTION: Tapered parts 62, 64 are provided in both end parts of a mandrel 60 which is used for extrusion. The outside diameter of the tapered parts 62, 64 is gradually made larger than specified outside diameter as approaching the end faces. Both end parts of the extruded tube 81 are thinned by tapered parts 62, 64, thus, thickening in both end parts of tube in rolling for reducing outside diameter with the stretch reducer is diminished.