A Chemically machinable photosensitive glass was shown to have a high potentiality as a material for new type particle track detectors. Micro crystals grow only along the alpha particle track in the glass through two steps of heat treatment, 500°C for 1h and 600°C for 5min, and the micro crystals grown in the glass are selectively etched in HF 3% solution. The etchpits are observed and counted using either scanning electron micrographs or an optical microscope with TV monitor. The proportionality of the number of etchpits to the alpha particle fluence is fairly good after the correction for the etchpits overlapping.