Plug flow of cohesionless granular material in a horizontal pipe was numerically simulated. The movement of each particle in a calculation region, which has periodic boundaries on its inlet and outlet, was solved. Contact force was modeled with springs, dashpots, and a slider. Repulsion force of the spring was given based on the contact theory of homogeneous isotropic elastic objects. The damping coefficient of the dashpot was given so as to make the coefficient of rebound constant. As a result, stable plug flow was observed in the present calculation. It is confirmed that the behavior of the plug and each particle is similar to the experimentally observed behavior.