A plastic working method of steel including austenite, the method comprising: physical property analyzing process of measuring Tp, σL β, and σH β for each of strain ratios β, when Tp represents a strain-induced-transformation-maximum-ductility-temperature in the unit of °C which is changed depending on the strain ratio β, σL β represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio β on a lower temperature side than the Tp, σH β represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio β on a higher temperature side than the Tp; deformation mode analyzing process of analyzing a strain ratio βx to be selected from among the strain ratios β, when the strain ratio βx is a strain ratio of an estimated breaking point which is specified during plastic deformation of the steel; heating process of heating the steel such that a local temperature T local is within a first temperature range indicated by the following expression 1 after selecting T βx from among the Tp, selecting σL βx from among the σL β, and selecting σH βx from among the σH β, when T βx represents a strain-induced-transformation-maximum-ductility-temperature in the unit of °C for the strain ratio βx, σL βx represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio βx on a lower temperature side than the T βx, σH βx represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio βx on a higher temperature side than the T βx, and the T local represents a local temperature (°C) of the estimated breaking point; and working process of plastically deforming the steel after the heating: T βx − 2 × σL βx ≤ T local ≤ T βx + 1.25 × σH βx physical property analyzing process of measuring Tp, σL β, and σH β for each of strain ratios β, when Tp represents a strain-induced-transformation-maximum-ductility-temperature in the unit of °C which is changed depending on the strain ratio β, σL β represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio β on a lower temperature side than the Tp, σH β represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio β on a higher temperature side than the Tp; deformation mode analyzing process of analyzing a strain ratio βx to be selected from among the strain ratios β, when the strain ratio βx is a strain ratio of an estimated breaking point which is specified during plastic deformation of the steel; heating process of heating the steel such that a local temperature T local is within a first temperature range indicated by the following expression 1 after selecting T βx from among the Tp, selecting σL βx from among the σL β, and selecting σH βx from among the σH β, when T βx represents a strain-induced-transformation-maximum-ductility-temperature in the unit of °C for the strain ratio βx, σL βx represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio βx on a lower temperature side than the T βx, σH βx represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio βx on a higher temperature side than the T βx, and the T local represents a local temperature (°C) of the estimated breaking point; and working process of plastically deforming the steel after the heating: T βx − 2 × σL βx ≤ T local ≤ T βx + 1.25 × σH βx