A positioner including a controlling portion for outputting, as a control output, an electric signal according to a difference between a valve opening setting value sent from a higher-level device and an actual opening value fed back from a regulating valve and an electric-pneumatic converting portion converting the control output from the controlling portion to an air pressure and for outputting the air pressure to a setting/operating device of the regulating valve, characterized in that the positioner comprises: a characteristic value/ambient temperature relationship storing portion storing a relationship between a characteristic value indicating sliding performance of a valve stem of the regulating valve, the sliding performance changing depending on an ambient temperature, and the ambient temperature; a control parameter storing portion storing correspondence between a level of the characteristic value and a control parameter used to control a valve opening of the regulating valve; a temperature sensor for measuring the ambient temperature at present of the regulating valve; a current characteristic value acquisition portion acquiring, as the characteristic value at present, the characteristic value corresponding to the ambient temperature at present of the regulating valve measured by the temperature sensor based on the relationship stored in the characteristic value/ambient temperature relationship storing portion; and a control parameter selecting portion selecting, from the control parameter storing portion, the control parameter corresponding to the level of the characteristic value at present acquired by the current characteristic value acquisition portion, wherein the controlling portion causes the current characteristic value acquisition portion to acquire the characteristic value at present and the control parameter selecting portion to select the control parameter corresponding to the level of the characteristic value at present repeatedly at regular intervals and the controlling portion is configured to control the valve opening of the regulating valve using the selected control parameter. a characteristic value/ambient temperature relationship storing portion storing a relationship between a characteristic value indicating sliding performance of a valve stem of the regulating valve, the sliding performance changing depending on an ambient temperature, and the ambient temperature; a control parameter storing portion storing correspondence between a level of the characteristic value and a control parameter used to control a valve opening of the regulating valve; a temperature sensor for measuring the ambient temperature at present of the regulating valve; a current characteristic value acquisition portion acquiring, as the characteristic value at present, the characteristic value corresponding to the ambient temperature at present of the regulating valve measured by the temperature sensor based on the relationship stored in the characteristic value/ambient temperature relationship storing portion; and a control parameter selecting portion selecting, from the control parameter storing portion, the control parameter corresponding to the level of the characteristic value at present acquired by the current characteristic value acquisition portion, wherein the controlling portion causes the current characteristic value acquisition portion to acquire the characteristic value at present and the control parameter selecting portion to select the control parameter corresponding to the level of the characteristic value at present repeatedly at regular intervals and the controlling portion is configured to control the valve opening of the regulating valve using the selected control parameter.