When simulating communication using a communication network such as a VoIP network, an actual communication state is accurately simulated, and communication is simulated. The distribution of delay times of packets is transformed by a predetermined transformation method, packet transmission timings to which delay times are added, are calculated based on the transformed distribution of delay times and predetermined transmission timings, a determination is made as to whether or not the packet transmission order is changed by the calculated transmission timings to which delay times are added, and, when a determination is made that the packet transmission order is changed, packet transmission timings adjusted so as not to cause a change in the transmission order are derived.