In this study, we propose a new acoustic model including the human ear canal and a thin tube earphone. The use of a tube earphone enables simultaneous listening of both virtual and real surrounding sound. First, we perform acoustic FDTD (finite difference time domain) simulations using an MRI head model with ear canals. The calculated external impedance viewed from the eardrum numerically shows that the influence of the inserted tube is small. A listening experiment with six subjects also confirms the effectiveness of a tube earphone. Second, we calculate HRTFs (head-related transfer functions) for eight directions in the horizontal plane to realize sound localization with a tube earphone. We also design inverse filters based on the propagation calculations including the characteristics of tube earphones. Finally we evaluate the localization system by another listening experiment with six subjects. The results reveal that the applicability of a system with tube earphones and inverse filters, particularly for the front directions.