To obtain a powdery glass ceramic material free from aggregation and easy to crush by wet-pulverizing a slurry prepared by adding water to coarse powder of a glass ceramic material, adding a nonaqueous solvent to the slurry and drying the slurry.

A slurry prepared by adding water to coarse powder of a glass ceramic material is pulverized to a prescribed particle diameter with a pulverizer such as a ball mill. A nonaqueous solvent is added to the resulting slurry and the slurry containing the aqueous-nonaqueous mixed solvent is dried. Since the water is removed together with the nonaqueous solvent by the azeotropic phenomenon of the mixed solvent, the re-solidification of the powder is prevented. Methanol or the like is used as the nonaqueous solvent and the amount of the solvent added is ≥10 wt.% of the water content of the slurry. The majority of the mixed solvent is evaporated in a low temperature part (50-90°C) in a 1st stage and the powder is sufficiently dried in a high temperature part (110-130°C) in a 2nd stage.