PURPOSE: To provide stepped grooves to glass with high precision and inexpensively by executing plural times of a series of procedure concerning exposure, crystallization, and etching to chemically grindable photosensitive glass by a specified process.

CONSTITUTION: A stepped hole is formed by the processes described hereunder wherein (A) a light exposed part 10 is formed by irradiating a chemically grindable glass 1 with light in the ultraviolet region (UV) through a first mask 2, (B) the exposed part 10 is converted to a zone for crystallizing lithium metasilicate 20 by heat-treating the glass at about 400W450°C, (C) then, the glass is irradiated with UV through a second mask 2' having a wider opening than the first mask 3 to form a second exposed zone 10' around the first crystallization zone 20, (D) the first crystallization zone 20 is dissolved and removed by treating the glass with dilute HF aq. soln, (E) a second exposed zone 10' is converted to a second lithium metasilicate crystallizing zone 20', then (F) one side of the glass is protected with a covering material 3 and the glass is treated from another side with dil. aq. HF soln. to dissolve the second crystallization zone 20' to a desired depth.