In this study, we applied a modified cruciform test to the evaluation of the interfacial tensile strength (IFTS) of the carbon fiber (CF)/polycarbonate (PC) interface and evaluated the effectiveness of the evaluation method via in situ observation. Although the interfacial shear strength has been extensively analyzed in previous works with thermosetting plastics, few studies have evaluated IFTS of thermoplastics, for instance, PC. However, previous reports have stated that the cruciform test is not suitable when the fiber transverse modulus is much lower than the matrix modulus. Therefore, in the present study, the modified cruciform test was carried out with specimen in which loading arms are reinforced with CF/PC cross-ply laminates in order to induce stress concentration at the fiber surface. Debonding was observed and was found to instantly propagate along the fiber, and the IFTS was calculated as 63.1±12.6 MPa on average. Thus, this investigation has revealed the IFTS of the CF/PC composite, and the effectiveness of the modified test to evaluate thermoplastic composites was confirmed.