This study investigates the causal effect of financial knowledge on short- and long-term financial behaviors across gender and age groups in Japan. Using a comprehensive survey conducted by the Bank of Japan, we construct financial knowledge and short- and long-term financial behavior indicators. Our results show that financial knowledge positively impacts short- and long-term financial behaviors. The evidence indicates that women are generally more financially responsible than men, although they are less likely to invest in financial assets. We also find that older individuals tend to practice more responsible financial behavior than younger ones. Additionally, the effects of financial knowledge on most financial behaviors decline as age increases, except for asset investment. We also find that the gender gap in financial behaviors is lower among those with higher financial knowledge. Our findings have significant policy implications for designing financial education programs.