Drastic grain comminution is frequently observed in upper-crust faults and large rock avalanche deposits. Here we report our model experiments to elucidate the possible role of grain comminution in dry granular friction. We sheared halite (NaCl) grains with a ring-shear configuration at a constant slip rate under various normal stresses and investigated the post-slip structures of the experimental fault zones using micro X-ray computed tomography. Consequently, distinct frictional behaviors were observed: a constant friction regime at small slip displacements and a frictional weakening regime at large displacements. The characteristic slip lengths for the two regimes decreased with increasing normal stress and were characterized by approximately the same exponent, regardless of the initial grain size. We developed a theoretical model that considered the production, saturation, and overflow of fine particles in the shear zone and successfully reproduced the transient frictional behavior in the experiments.