This paper proposes a numerical simulation method for the dynamic motion of a flexible riser pipe undergoing vortex-induced vibration (VIV). The method is based on a finite difference scheme for solving nonlinear structural dynamics of the pipe and wake oscillator model for quantifying vortex-induced forces acting on the pipe, the combination of which can offer a very efficient and stable computation. To investigate the accuracy of the method, we performed simulations of the VIV of riser pipes under uniform flow and sheared flow conditions; and then compared obtained results with experiments of preceding works. We consequently confirmed that the present method can simulate a couple of important aspects of the VIV of the pipes: frequency, mode shape, and amplitude of displacement of cross-flow displacement.