to an increased inner pressure and the softening of the glass tube 21 as shown in the right in fig2 and fig3 a after the deformation of the glass tube 21 the glass tube 21 with the shaping unit 22 is cooled a flat elliptic glass tube 23 is thereby formed since the glass tube is more rapidly cooled than air in the tube in the cooling process the glass tube 23 maintains its flat elliptic cross sectional shape preferably the maximum temperature of the heating furnace is in the range of 600 u00b0 c to 720 u00b0 c for pyrex glass or is in the range of 70 to 90 of the softening point for other glass materials referring to fig3 b the glass tube 21 that is placed into the shaping unit 22 may have an outer diameter larger than the short side of the shaping unit 22 in such a case the glass tube 21 in the shaping unit 22 is placed in the heating furnace in a state that one side plate 22 a of the shaping unit 22 is separated from other portions a predetermined pressure 25 applied from the side 22 a causes deformation of the softened glass tube 21 into a flat elliptic cross sectional shape along the cross sectional shape of the shaping unit 22 referring to the left in fig3 c alternatively a flat elliptic glass tube 26 may be used for forming the flat elliptic glass tube 23 having a desired cross sectional shape in this embodiment the both sides of the glass tube placed into the shaping unit are preliminarily sealed alternatively an open glass tube may be used in such a case the open glass tube is placed into the shaping.