In this study, the diametrical compression test was carried out using Inada granite by attaching strain gages to the test specimen.Young's modulus under tensile stress was estimated from the value of the measurement of the strain. The results obtained through this study are as follows:1) It is deemed that Young's modulus under tensile stress can be estimated from the diametrical compression test results by the method shown in this research.2) The standard deviation of tensile strain was calculated. The results showed that standard deviation increases rapidly, once the tensile stress exceeds a certain value. It is considered that the stress of a tensile fracture area differs within a test specimen if the load increases. Therefore, if tensile strength estimates from St=-2P/πDL use maximum load, it is possible that tensile strength was overestimated.