A variety of electronic cigarettes (e-cigarettes) are sold in Japan and targeted toward young people. However, few studies have considered who uses e-cigarettes and why they use them. This study examined factors associated with e-cigarette use and the reasons for their use among the young population in Japan. Our internet-based cross-sectional study was conducted between February and March 2019. We analyzed the data of 2,414 participants aged 15-29 years to identify factors associated with e-cigarette use in the last 12 months and assess the reasons participants gave for their use. We found 4.3% of the participants had used e-cigarettes in the past 12 months. The multivariable logistic regression showed that the use of combustible or heated tobacco and perceiving e-cigarette use as an attractive behavior were associated with having used e-cigarettes. Interest in fruit flavors, stylish design and function of e-cigarettes, and the influence of friends using e-cigarettes were major reasons for their use. Although e-cigarette users are still a minority among this population, the flavors and design of e-cigarette products attract young people, and gain popularity in the youth community. This highlights an urgent need for the monitoring of e-cigarette and tobacco use among the young population in Japan.