A temperature abnormality detection method for protecting a power conversion device provided with a power conversion unit that converts and transmits electric power, and a cooling fluid flow path that cools the power conversion unit , the method comprising: a difference calculation step (S12) for calculating a difference (ΔT1) between a power conversion unit temperature (Tin1), which is a temperature of the power conversion unit , and a cooling fluid temperature (Tw) of the cooling fluid flow path ; characterized by a first abnormality determination step (S13) for determining that a temperature abnormality exists when: the difference (ΔT1) exceeds a preset difference threshold (ΔTfaill1), and the power conversion unit temperature (Tin1) exceeds a first power conversion unit temperature threshold (Tinfail1); and a second abnormality determination step (S14) for determining that a temperature abnormality exists when: the first abnormality determination step did not determine that a temperature abnormality exists, and the power conversion unit temperature (Tin1) exceeds a second power conversion unit temperature threshold (Tinfail2) set to a higher value than the first power conversion unit temperature threshold (Tinfail1); when a temperature abnormality is determined in either the first (S13) or the second (S14) abnormality determination step,a preset protective operation process is executed (S15) and the protective control is ended.). a difference calculation step (S12) for calculating a difference (ΔT1) between a power conversion unit temperature (Tin1), which is a temperature of the power conversion unit , and a cooling fluid temperature (Tw) of the cooling fluid flow path ; characterized by a first abnormality determination step (S13) for determining that a temperature abnormality exists when: the difference (ΔT1) exceeds a preset difference threshold (ΔTfaill1), and the power conversion unit temperature (Tin1) exceeds a first power conversion unit temperature threshold (Tinfail1); and the difference (ΔT1) exceeds a preset difference threshold (ΔTfaill1), and the power conversion unit temperature (Tin1) exceeds a first power conversion unit temperature threshold (Tinfail1); and a second abnormality determination step (S14) for determining that a temperature abnormality exists when: the first abnormality determination step did not determine that a temperature abnormality exists, and the power conversion unit temperature (Tin1) exceeds a second power conversion unit temperature threshold (Tinfail2) set to a higher value than the first power conversion unit temperature threshold (Tinfail1); when a temperature abnormality is determined in either the first (S13) or the second (S14) abnormality determination step,a preset protective operation process is executed (S15) and the protective control is ended.). the first abnormality determination step did not determine that a temperature abnormality exists, and the power conversion unit temperature (Tin1) exceeds a second power conversion unit temperature threshold (Tinfail2) set to a higher value than the first power conversion unit temperature threshold (Tinfail1); when a temperature abnormality is determined in either the first (S13) or the second (S14) abnormality determination step,a preset protective operation process is executed (S15) and the protective control is ended.). <EOS>