The micelle formation in amphiphilic solution is investigated by means of a molecular dynamics simulation of coarse-grained amphiphilic molecules with explicit solvent molecules. A random configuration of amphiphilic molecules in solution at high temperature is quenched to a lower temperature. Our simulations show that the micellar shapes change from a cylindrical micelle to a planar bilayer as the number density increases. At higher densities, we also find the following characteristic features. (1) The potential energy relaxes in a stepwise manner. (2) The radius of gyration Rg of the largest micelles increases with time in a stepwise fashion. (3) The sharp bumps in Rg occur during coalescence of micelles.