A (Nb, Ti) phase in an Nb--Ti--Co alloy is composed of a granular structure. The Nb--Ti--Co alloy is preferably subjected to heat treatment at 800.degree. C. or more so that the eutectic structure in the casted state can be changed to a granular structure. The Nb--Ti--Co alloy used there is preferably Nb.sub.xTi.sub.(100-x-y)Co.sub.y, (x.ltoreq.70, 20.ltoreq.y.ltoreq.50 (mol %)). By properly predetermining the heating temperature and time, the resulting alloy exhibits improved hydrogen permeability in combination with a good hydrogen embrittlement resistance characteristic in the CoTi phase, making it possible to provide a practical hydrogen permeable membrane having an advantageously high performance.