In this study, the stress dependence of the Barkhausen noise (BHN) signal is investigated in samples of a spheroidized cementite carbon steel of 0.1-0.5 mass% C, and the mechanism of the dependence on stress is clarified and related to the microstructure of the steel. When the carbon content of the test pieces is higher, the variation in root mean squared (rms) value of the BHN signal when the sample is stressed becomes larger; the rate of change reaches 52.8% in the 0.5% C sample in the stress range from 50 MPa to -200 MPa. Two new models have been adopted to explain the behavior of the BHN signal under stress conditions: the first explains how the magnetic field of reverse domain generation decreases with increasing magnitude of compressive stress, and the second model explains why the number of 90° domains increases as a result of transitions from 180° domains. According to these models, when a compressive stress is applied, the internal tensile stress within the ferrite due to the difference in thermal expansion between cementite and ferrite inhibits the decrease in the magnetic field of reverse domain generation and results in an increase in the number of 90° domains. Since it is clear from the conventional Gaussian pulse model that these inhibiting effects increase the rate of change in the rms value of the BHN signal, the greater internal tensile stresses in higher carbon steels can therefore explain the increase in the rate of change in the rms value as the external compressive stress increases.