A new particle simulator to analyze the behavior of carrier beads around a magnet roll in a two-component developer unit in electrophotography has been developed. The simulator, which is based on the Discrete Element Method, including the magnetic interaction force among particles in a magnetic field, adopts parallel processing with MPI and/or OpenMP. Parallel processing of the particle simulator with several processors provides excellent performance to simulate the behavior of a realistic amount of particles in a practical time. The simulation results obtained for tens of thousands of carrier beads reveals not only realistic particle behavior around a magnet roll but also the quantitative relation between the stress on the carrier and the amount of carrier beads that passes through a gap between the doctor blade and the magnet roll. These are very important parameters to obtain high-quality images in a two-component developer unit.