To estimate the volume fraction of martensite induced in 304ss type austenitic stainless steel during tensile deformation, the electric resistance of the specimen was measured using the four-point-probes method at the temperatures of 77, 196 and 293K during the deformation. The magnetic force of the deformed specimen was also measured using a permanent magnet to determine the strain at which the martensite was induced initially in the specimen. The parallelepiped model was suggested to separate the effects of the deformation and transformation on the electric resistivity because the resistivity was influenced by the evolution of the martensite and the growth of the defect in the matrix at a constant temperature. The parallelepiped model consisted of m columns with n pieces of the cubic element and was assumed to be a group of small electric resistors. The volume fraction of the martensite estimated using the measured resistivity and the model was compared with the experimental results reported by other researchers and then it was clarified that the volume fraction of the martensite estimated by the model was in agreement with the volume fraction measured by the experiment.