A wind tunnel experiment using a SDOF circular cylinder tower model was conducted to study the characteristics of the vortex-induced vibration which occurs at a wind speed higher than the occurrence wind speed of the ordinary vortex-induced vibration. Across-wind model response and the fluctuating wind velocity behind the model at various heights were measured. Wavelet analysis was applied to the data of the fluctuating wind velocity behind the model. The wavelet analysis clarified that the tip-associated vortex is formed rather intermittently around the model top and this causes that vibration. The amplitude of that vibration possesses a slight modulation due to the intermission of the tip-associated vortex.