In order to survey the wind characteristics of Japan, where mountainous terrain is predominant, a large amount of wind data (NEDO Field Test Data) from more than 300 measurement sites in Japan were analyzed in detail, particularly the turbulence characteristics. As a result, it was found that the profiles of the 90% quantiles of turbulence intensity estimated in all of the NEDO Field Test Data are well approximated by the IEC Normal Turbulence Model (NTM). However, the turbulence intensity levels of more than 65% of the measurement datasets exceed the most severe turbulence category (Category A) in IEC 61400-1 (Ed.3). We therefore conclude that the present IEC turbulence model for wind turbine design does not reflect the severe wind conditions of mountainous countries such as Japan. This is considered to be one of the main reasons for the frequent problems of wind turbines in Japan. New criteria for the NTM are proposed to overcome this problem. The appropriateness of the new criteria to the severe wind characteristics in Japan is also discussed.