To provide a method for treating the inside surface of a glass tube which is capable of obtaining a smooth inside surface of the glass tube by preventing the etching dust from sticking to the inside surface.

When etching the inside surface of a glass tube 31 by heating the glass tube 31 through reciprocating a heat source 33 relatively against the glass tube 31 and from upstream to downstream along the length of the glass tube 31 while flowing an etching gas 32 through inside of the glass tube 31, the heat source 33 is shut OFF in the downstream side after the etching treatment has been finished via the required number of times of reciprocating of the heat source 33 and in that when the heat source 33 is shut OFF, the supply of the etching gas 32 is simultaneously shut off.