In order to investigate the relation between a stress cycle and a temperature change of metallic materials, a computer-aided platinum wire temperature measurement system was used for taking the data of temperature, stress and strain into the computer memory simultaneously. Fatigue tests have been conducted using the smooth round bar specimen made of carbon steels (S55C, SCM435) and stainless steels (SUS304). The temperature changes under an elastic stress range are agreed well with the value calculated by the thermo-elastic theory. On the other hand, the temperature changes under a plastic stress range are larger than the calculated values, because of the plastic stress-strain works. As the result, the crack initiation life is explained by the equations ; S55C material : Δq · Nc = 1.5 × 109J/m3, SCM435 : Δq · Nc = 2.6 × 108J/m3, SCM435 Material : Δq · Nc = 9.0 × 108J/m3.