The authors implemented artificial compressibility method (ACM) with virtual flux method (VFM) on a GPU to simulate incompressible unsteady state flow fields around a cylinder, and lattice Boltzmann method (LBM) on a GPU to simulate incompressible turbulent flows. In this study, unsteady flow fields around a circular cylinder were calculated by LBM with VFM. The history of the length of twin vortex behind a circular cylinder and the Strouhal number were compared with that of the other researchers; also, the speedup obtained by a GPU is shown.