A temperature measuring method of measuring the temperature of a steel sheet, said temperature measuring method comprising the steps of: disposing a reference plate provided with a temperature controller facing said steel sheet; directly measuring the reference plate temperature T 2 of the reference plate by a thermometer other than a radiation pyrometer; directing a radiation pyrometer on the steel sheet at an angle such that alternate reflection of radiation energy by the reference plate and the steel sheet occurs once or twice, for measuring a radiosity of the steel sheet; executing a closed-loop control operation by the temperature controller to make the reference plate temperature T 2 approach the steel sheet temperature and coincide with an approximate temperature T 1 ' of the steel sheet temperature, the approximate temperature T 1 ' of the steel sheet being calculated by using: T 1 ' = T g + K T g − T 2 where K is a correction coefficient determined on the basis of estimated values of the respective emissivities of the reference plate and the steel sheet, and T g is a radiosity temperature, obtained by measuring the radiosity of the steel sheet by the radiation pyrometer; and using a temperature obtained by converting the radiosity into a temperature of a blackbody that radiates energy equivalent to the radiosity as the radiosity temperature T g, wherein the radiosity temperature T g changes as the closed loop control operation is executed, such that a difference ΔT between T 2 and T g decreases gradually and approaches 0, and achieving a measurement of the temperature of the steel sheet by regarding the approximate temperature T 1 ' to be the temperature of the steel sheet. disposing a reference plate provided with a temperature controller facing said steel sheet; directly measuring the reference plate temperature T 2 of the reference plate by a thermometer other than a radiation pyrometer; directing a radiation pyrometer on the steel sheet at an angle such that alternate reflection of radiation energy by the reference plate and the steel sheet occurs once or twice, for measuring a radiosity of the steel sheet; executing a closed-loop control operation by the temperature controller to make the reference plate temperature T 2 approach the steel sheet temperature and coincide with an approximate temperature T 1 ' of the steel sheet temperature, the approximate temperature T 1 ' of the steel sheet being calculated by using: T 1 ' = T g + K T g − T 2 where K is a correction coefficient determined on the basis of estimated values of the respective emissivities of the reference plate and the steel sheet, and T g is a radiosity temperature, obtained by measuring the radiosity of the steel sheet by the radiation pyrometer; and using a temperature obtained by converting the measuring the radiosity of the steel sheet by the radiation pyrometer; and using a temperature obtained by converting the radiosity into a temperature of a blackbody that radiates energy equivalent to the radiosity as the radiosity temperature T g, wherein the radiosity temperature T g changes as the closed loop control operation is executed, such that a difference ΔT between T 2 and T g decreases gradually and approaches 0, and achieving a measurement of the temperature of the steel sheet by regarding the approximate temperature T 1 ' to be the temperature of the steel sheet.