This study discussed effects of individuals' impulsiveness and deliberation on decision-making behavior. Our research questions are as follows: (1) Does impulsiveness relate to risk-taking behavior in decision-making? (2) Do impulsiveness and deliberation affect distinctiveness in decision-making? In the experiments, participants were required to choose from two options: a gambling option with a probability of winning and a sure option. When the sure option was selected, participants obtained the presented amount of hypothetical money surely. When the gambling option was selected, the amount of hypothetical money obtained was determined by chance (the probability was presented on a pie chart). The results are as follows. First, participants with high impulsiveness tended to overestimate objective probability more than those with low impulsiveness. Second, when decision time was restricted, participants with high impulsiveness could not clearly discriminate between changes in probability. This tendency of participants with high impulsiveness when decision time was restricted improved when they were told that focusing on a series of selection results would obtain an optimum result.