A flow rate measuring system, comprising: - a measuring mechanism adapted to measure at least one of a radiation coefficient or a value for thermal conductivity for a measured mixed gas, - a flow rate sensor adapted to detect a flow rate of the measured mixed gas, calibrated using a calibration gas, and - a correcting portion adapted to correct a detection error in the flow rate, characterized: - in that said measuring mechanism is adapted to measure the at least one of a radiation coefficient or a value for thermal conductivity for a measured mixed gas when a heater element (61 A) has produced heat at a plurality of heat producing temperatures; - by a thermal diffusivity calculating equation storing device storing a thermal diffusivity calculating equation that uses at least one of the radiation coefficients or the thermal conductivities for the plurality of heat producing temperatures as independent variables and uses a thermal diffusivity as a dependent variable; - by a thermal diffusivity calculating portion adapted to calculate a value for the inverse 1/α of the thermal diffusivity of the measured mixed gas through substituting the values of at least one of the radiation coefficients (M I) or the thermal conductivities of the measured mixed gas for the plurality of heat producing temperatures (T H1, T H2, T H3, T Hn-1), for the independent variables of at least one of the radiation coefficients or thermal conductivities, for the plurality of heat producing temperatures, in the thermal diffusivity calculating equation; - in that the flow rate sensor includes a microchip that comprises a heater and a temperature measuring element; and - in that said correcting portion is adapted to correct a detection error in the flow rate due to a difference between the value for the inverse of the thermal diffusivity of the calibration gas and the value for the inverse of the thermal diffusivity of the measured mixed gas. - a measuring mechanism adapted to measure at least one of a radiation coefficient or a value for thermal conductivity for a measured mixed gas, - a flow rate sensor adapted to detect a flow rate of the measured mixed gas, calibrated using a calibration gas, and - a correcting portion adapted to correct a detection error in the flow rate, characterized: - in that said measuring mechanism is adapted to measure the at least one of a radiation coefficient or a value for thermal conductivity for a measured mixed gas when a heater element (61 A) has produced heat at a plurality of heat producing temperatures; - by a thermal diffusivity calculating equation storing device storing a thermal diffusivity calculating equation that uses at least one of the radiation coefficients or the thermal conductivities for the plurality of heat producing temperatures as independent variables and uses a thermal diffusivity as a dependent variable; - by a thermal diffusivity calculating portion adapted to calculate a value for the inverse 1/α of the thermal diffusivity of the measured mixed gas through substituting the values of at least one of the radiation coefficients (M I) or the thermal conductivities of the measured mixed gas for the plurality of heat producing temperatures (T H1, T H2, T H3, T Hn-1), for the independent variables of at least one of the radiation coefficients or thermal conductivities, for the plurality of heat producing temperatures, in the thermal diffusivity calculating equation; - in that the flow rate sensor includes a microchip that comprises a heater and a temperature measuring element; and - in that said correcting portion is adapted to correct a detection error in the flow rate due to a difference between the value for the inverse of the thermal diffusivity of the calibration gas and the value for the inverse of the thermal diffusivity of the measured mixed gas. - in that said measuring mechanism is adapted to measure the at least one of a radiation coefficient or a value for thermal conductivity for a measured mixed gas when a heater element (61 A) has produced heat at a plurality of heat producing temperatures; - by a thermal diffusivity calculating equation storing device storing a thermal diffusivity calculating equation that uses at least one of the radiation coefficients or the thermal conductivities for the plurality of heat producing temperatures as independent variables and uses a thermal diffusivity as a dependent variable; - by a thermal diffusivity calculating portion adapted to calculate a value for the inverse 1/α of the thermal diffusivity of the measured mixed gas through substituting the values of at least one of the radiation coefficients (M I) or the thermal conductivities of the measured mixed gas for the plurality of heat producing temperatures (T H1, T H2, T H3, T Hn-1), for the independent variables of at least one of the radiation coefficients or thermal conductivities, for the plurality of heat producing temperatures, in the thermal diffusivity calculating equation; - in that the flow rate sensor includes a microchip that comprises a heater and a temperature measuring element; and - in that said correcting portion is adapted to correct a detection error in the flow rate due to a difference between the value for the inverse of the thermal diffusivity of the calibration gas and the value for the inverse of the thermal diffusivity of the measured mixed gas.