1. A simulation device which simulates motion of a robot system comprising a plurality of robots each comprising a drive shaft driven by a motor, the simulation device comprising: a simulation unit which executes, by simulation, a motion program for each robot in which each robot is set in advance so as not to interfere with one another, the motion program containing a command velocity and a command acceleration of the drive shaft, and a motion waiting instruction; a storage unit which stores in time series a line number of the motion program and the command velocity and the command acceleration at the line number associated with one another; an execution time calculation unit which calculates an execution time of the motion program for each of the line numbers stored in the storage unit based on a simulation result obtained by the simulation unit; and a waiting time calculation unit which calculates a motion waiting time in accordance with the motion waiting instruction based on the execution time calculated by the execution time calculation unit.