Granite and quartz were crushed under moist conditions in the temperature range of 25--270 ¿C, in order to obtain the information on the mechanism operative for H2 degassing along active faults. It was found that the amounts of H2 gas released by crushing granite and quartz increased with temperature up to around 200 ¿C and then decreased suddenly. The results indicate that H2 gas is generated by a chemical reaction between water and such radicals as Si⋅ and Si--O⋅ formed on the fresh surfaces when the Si--O--Si bonds are destroyed by crushing and that the existence of a maximum for anount of H2 gas is due to the decrease of the lifetime of Si--O⋅ radical at the temperature higher than about 200 ¿C. The results lend credence to the possibility that H2 gas is generated in the temperature range of 25--270 ¿C along the active fault through the reaction between groundwater and the fresh surfaces of underground rocks formed by the fault movements.