To provide a glass compound capable of forming a glass tube by a conventional tube-drawing process such as a Velo process or Danner process and giving glass tubes ideally having very little tendencies to cause deformation (shrinkage and bending) and to stick with each other at a processing temperature up to 700°C in a subsequent process.

The borosilicate glass includes, in terms of mol% of oxide, SiO₂ 74-81, B₂O₃ 8.5-14.5, Al₂O₃ 0.5-3.5, Na₂O 1.5-3.5, K₂O 1.0-2.0, Li₂O 0-1.0, MgO 0.5-1.5, CaO 0.5-1.5, BaO 0-0.6, TiO₂ 2.0-3.5 and ZrO₂ 0-1.0 and, as a clarifier, Sb₂O₃ 0-0.15, CeO₂ 0-0.5 and SnO₂ 0-0.5 and has the molar ratio satisfying 0.4<Na₂O/(Na₂O+K₂O)≤0.72.