In the intuitive probability judgment, two approaches to explain “conjunction fallacy" and “base rate fallacy" have been discussed in previous studies. The first is the heuristics approach (Tversky & Kahneman, 1974), and the second is conversation convention approach (Grice, 1975). The present article discussed theoretical limitations of each approach. Integrating these two approaches, the present article proposes a third approach,“problem-solving approach". This approach stresses the importance of how subjects perceived the given problem, so that the flexibility of judgment and the dependency of content/context could be attributed to their mental model.