The effects of low level alcohol in man were studied by several psychophysiological tests. Five male college students were tested on the battery of mental tasks involving Dot-Matrix, Signal Sound Detection, Choiced Reaction Time at three levels (33.5, 67.0, 134.0 ml : whisky) of alcohol dose. Alcohol concentration in breath, critical flicker fusion, heart rate and blinking counts were measured. Results obtained are as follows. 1) Increase in the alcohol concentrations in breath and heart rate, decrease in the blinking counts are shown in proportion to alcohol dose level. 2) Alcohol effcts of least dose (33.5 ml) in this experiment are shown clearly on the condition of adding two subsidiary tasks to the main task. The results of this study suggest that the complex-task-method is useful to estimate the effects of low level alcohol to the psychophysiological functions in man.