＇Granular convection＇ is a well-known phenomenon when particles in a bin are vertically vibrated. However, the actual mechanical movement is not yet fully understood. An experiment using magnetic resonance image (MRI) by Ehrichs et al., clearly reveals the behavior of particles. In this study the experiment is simulated using a three-dimensional distinct element code. The analytical result, shown as a central section of the particle layers, is identical to the experimental one. A comparison between the 0-4 cycles and 100-104 cycles reveals a similar behavior. This demonstrates that convection occurs as a repetition of 1 cycle. Detailed analysis reveals the behavior of the individual particles during convection. The driving force of the convection appears to be a different movement of the inner and outer particles. This mechanism proposed by Taguchi is proved by this analysis.