The vertical pneumatic conveying of granules was performed experimentally in order to investigate the effect of spiral flow on the damage of granules. The spiral flow used in this study is weak and the maximum swirl number is 0.03 when the mean air velocity is 10m/s. It was found that granules are transported along the pipe wall in the spiral flow and the spiral flow is effective in reducing the damage of granules at lower air velocity. Numerical simulations showed that the number of collisions between granules and pipe wall in the spiral flow is larger than that in the axial flow but the kinetic energy of granules that come in collision with the pipe wall is smaller in the spiral flow than in the axial flow at lower air velocity. It is inferred that the spiral flow makes the granules move along the pipe wall reducing the kinetic energy of granules to below the threshold of granule strength for breakage.