The authors examined participants' preferences between certain and uncertain outcomes in a multistage gambling task and the effects of individual difference characteristics on those preferences. In Study 1, 144 participants made choices in single-stage gambles under gain and loss conditions and replicated the certainty effect in a previous study (D. Kahneman & A. Tversky, 1979). In Study 2, 94 participants engaged in a multistage gambling task using the same decision problems as those in Study 1. They also answered a questionnaire consisting of the Japanese version (M. Kamahara, K. Higuchi, & N. Shimizu, 2001) of the Locus of Control Scale (J. B. Rotter, 1966), the Reflection-Impulsivity Scale (K. Takigiku & A. Sakamoto, 2001), and a Japanese version (M. Terasaki, K. Shiomi, Y. Kishimoto, & K. Hiraoka, 1987) of the Sensation-Seeking Scale (M. Zuckerman, 1994). The results indicated that the certainty effect (Kahneman & Tversky) disappears in multistage gambling tasks and that differences in reflection-impulsivity and in gender influence the process of decision making under gain conditions. These results are discussed in terms of the decision strategies and cognitive biases involved in the multistage gambling task.