In this paper, we investigated the factors affecting the intention to use smartphone banking with a research model based on the Technology Acceptance Model (TAM) extended to include security risk, trust, and self-efficacy. With analysis after controlling factors such as age, gender, and previous experience of smartphone banking that may have effects, we conclude that perceived usefulness, perceived ease of use, security risk, and trust have direct effect on the intention to use smartphone banking, and self-efficacy has indirect effect on the intention to use through mediation of perceived ease of use. We performed a study to check the validity of TAM in the context of smartphone banking, and confirmed that perceived ease of use has both direct and indirect effect on the intention to use.