A glass substrate having fine holes formed therein by use of a laser beam without cracks or fragmentation occurring. A glass substrate is used in which silver is contained in the form Ag atoms, Ag colloid or Ag ions, to a predetermined depth from a surface of the glass, and further the concentration gradient of the silver is a maximum at one side surface on which the fine hole machining is performed and gradually decreases toward the other side surface, whereby ablation and evaporation occurs from the surface having the maximum concentration of silver layer by layer without causing cracking or fragmentation.