Large Eddy Simulation (LES) is expected to be adopted as an effective technique to evaluate wind load on buildings for wind-resistant design. For numerical prediction of wind pressures by LES, unstructured grid system is effective in terms of flexibility in generating computed models. In this paper, the fluctuating wind pressures on a high-rise building influenced by windward building are examined using unstructured LES. Especially, focusing on the critical phenomena regarding pressure intensification, the availability of LES is examined by comparison with experiments and the flow fields are studied to elucidate the mechanism of peak pressure occurrence.