In this research, we propose a high-speed simulator for rapidly determining protocol performance of a sensor network comprised of many terminals. We have developed this simulator by using GPGPU technology[1], in which widely used GPUs (Graphics Processing Units) are applied to general-purpose computing. This simulator executes at high-speed by using the parallelism that is a structural feature of GPUs, and enables simultaneous execution of simulations with various values of the parameters in the protocol. The result is high-speed simulations using inexpensive hardware which previously could only be processed using a supercomputer.