X-ray computed tomography (CT) is widely used for three-dimensional nondestructive X-ray imaging of the internal structure of the human body or industrial materials. For modern technology in the medical field, dual-energy CT (DE-CT) with two types of X-ray effective energy has generally been used. However, the X-ray signals of DE-CT are integrated and read out in the form of a current. Thus, contamination with dark noise significantly degrades such imaging qualities as contrast, which causes a large radiation dose to patients. In addition, little energy information on DE-CT results in poor material discrimination of target materials. Recently, the photon-counting CT (PC-CT) system has developed for future CT technology. Because the PC-CT system can detect individual X-ray photons, the dark-noise effect expected to be highly suppressed. The multiple energy data obtained by PC-CT provide fruitful information on the energy dependence of the CT values, leading to high potential for material discrimination. Thus, an MPPC-based PC-CT system combined with high-speed scintillators has been proposed, and a 64-channel CT array system was developed recently. In this study, the details of the performance estimate of the MPPC-based PC-CT system were investigated in terms of energy information and photon-counting capability. The initial results of the CT image contrast compared with the clinical DE-CT system are presented. They show that the proposed PC-CT system achieved a similar contrast-to-noise ratio value to that of the clinical DE-CT.