Elevators can be regarded as oscillators driven by the calls of passengers who arrive randomly. We study the dynamic behavior of elevators during the down peak period by simulation and analytical calculation. We assume that new passengers arrive according to a Poisson process on each floor and call the elevators to go down to the ground floor. We numerically examine how the round trip time depends on the inflow rate of passengers on each floor and reproduce it by an equation considering the combination of floors where call occurs. We also examine the degree of the synchronization of two elevators by setting an order parameter.