The purpose of this study was to examine the effects of time pressure (TP) on the speed of stimulus evaluation and processing resources, and speed and accuracy of the behavioral response, using P300. The participants were 13 physical education students (mean age 18.85 years, SD 0.95), who were presented with a flanker task involving spacing between letters. Under non-TP conditions, there was no feedback sound even if there was no reaction before the stimulus was replaced by a new stimulus. The TP condition was a feedback sound that was triggered if no reaction occurred within 350 ms. The results showed that in terms of behavioral parameters, the reaction time became shorter with increasing TP. In addition, response accuracy decreased with increasing TP. Among physiological indices, P300 latency at Pz was shorter and P300 amplitude at Pz was larger under TP conditions than under non-TP conditions. Our results suggest that TP shortens the process of stimulus evaluation, and that more processing resources are required under TP conditions.