Nonlinear behavior of the resistive wall modes (RWMs) has been studied using nonlinear three-dimensional simulation code based on the reduced magnetohydrodynamic equations in a cylindrical tokamak. The vacuum is replaced by a highly resistive plasma using the pseudo-vacuum model. For the case that the RWM with $(m,n)\,{=}\,(3,1)$ mode and the internal $(m,n)\,{=}\,(5,2)$ mode are unstable, the RWM with $(m,n) \,{=}\, (3,1)$ mode enhances the growth rate of the internal $(m,n)\,{=}\,(5,2)$ mode in the nonlinear phase. The magnetic field line stochastization is obtained around the plasma edge due to the overlapping of the magnetic islands of the $(m,n)\,{=}\,(3,1)$ mode and the $(m,n)\,{=}\,(5,2)$ mode.