This study analyzed the factors that determine individual investors' investment decisions when purchasing substitute stocks during a bull market, as well as the factors they consider when selecting investment stocks. An empirical analysis was conducted on individual investors' switching intention to substitute stocks and the factors they consider, and based on these empirical results, the study attempted to identify variables influencing individual investors' rational investment decision-making and to provide a theoretical approach to stock investment switching intention. The empirical analysis results showed that alternative attractiveness, alternative risk, risk propensity, and information search desire had significant effects on the intention to switch to substitute stocks. When switching to substitute stocks, investors were found to consider corporate growth potential, corporate technical analysis, stock market conditions, institutional investor trends, financial statement analysis, and rumors/disclosures. A comparison of index stock returns and substitute stock returns during a bull market revealed that, as expected, index stock returns were higher.