The dynamics of internal waves in a small caldera lake, Lake Kuttara, Hokkaido was examined for the period of September-October 1989, by means of the FFT spectral analysis of time series of water level, water temperature, flow velocity and meteorological conditions. The lake during that period was thermally stratified, but the epilimnion decreased water temperature due to convective cooling. Spectral analysis of water level, water temperature and flow velocity revealed that a lake-current system below the thermocline is characterized by periodic free motions due to rotational internal waves. Meanwhile, a wind system over the lake consisted of daily land-sea breezes and some episodic events due to cyclone lows. The former is characteristic of the lake near the Pacific Ocean. It was oberved that an internal wave rotating counterclockwise or clockwise with periods of 3.1-3.3 hr is induced by both relatively strong sea breezes and episodic eastern-wind events, whereas in the episodic events, an internal wave rotating clockwise with a period of 2.7 hr simultaneously prevails.