The importance of humanitarian access has been widely recognized by practitioners and scholars. Nevertheless, the factors behind its success have been not yet fully clear. This study, therefore, conducted a quantitative analysis of the International Committee of the Red Cross's (ICRC) access to detainees' visits to elucidate the success factors of humanitarian access. It analyzed a government's attributes that grant the ICRC access and engagements to soften the government's refusal of its access. The results revealed the following findings: (1) a government's capacity is required to an extent to keep public services in armed conflict; (2) material incentive (MI) in a government is working, and the ICRC assistance for civilians is effective; (3) conceptual incentive (CI) to seek the international legitimacy is irrelevant; (4) conceptual disincentive (CD) to avoid disclosure of the government's violation of humanitarian norms is working, and a high-level meeting with the ICRC is less likely to lessen the government's concern. These findings supplement insights of previous research on general humanitarian access in a quantitative way, implying the possibilities and the limits of humanitarian agency's engagements. Further research on various types of humanitarian success can clarify its success factors in a more specific way.