We compared the calculation performance of cosmological N-body simulations with and without GRAPE-4. A modified Barnes-Hut treecode was used for these simulations. GRAPE(GRAvity piPE) is a special-purpose computer for gravitational N-body simulations. The newest hardware GRAPE-4 achieved a quite high peak performance (1.08 Tflops). In cosmological N-body simulations, a large number of particles is required and fast algorithms such as Barnes-Hut treecode or P3M/PM are usually used. GRAPE-4 can accelearte such algorithms. In paticular, the PCI interface recently completed allows us to use fast host computer, thus it improved the performance of these fast algorithms. Figure 1 shows the CPU time per one timestep as functions of force calculation error for both systems with and without GRAPE-4.