When a current applied to an intrinsic Josephson junction (IJJ) in a copper oxide high-temperature superconductor is increased, the IJJ enters a voltage state and then the voltage increases stepwise. After these voltage states, when the current is lowered, THz oscillation occurs. The voltage state is described as a running state of a particle in a washboard potential, using the RCSJ model of the Josephson junction (JJ). In this study, we investigate these running states in the IJJ, using a coupled layered JJ model with the finite element method. Especially, we focus on time evolution of phase differences in all JJs in the IJJ under weak external current.