PURPOSE: To prevent the falling of fine glass powder into the drug solution in the cutting of the neck of a glass ampule having double-walled structure, by reforming the main body with rollers under heating so as to adjust the outer diameter of the main body to be matched with the inner diameter of the outer tube, and fitting and welding the outer tube to the main body.

CONSTITUTION: A double-walled ampule made of glass, etc. is manufactured by welding the cap 2 to the main body 1. The main body 1 is reformed beforehand with the rollers 4, 5 under heating with a burner to adjust the outer diameter to be matched with the inner diameter of the cap 2, and then the cap 2 is fitted to the reformed part of the main body 1 When the rollers 4, 5 are furnished with ridges 6, the fixing and welding can be carried out more firmly.