1. An electronic clinical thermometer for predicting an equilibrium temperature based on a temporal change in actual measurement value of a measurement target temperature detected by a temperature detection element, comprising: determination means for determining, based on temperature rise rate detected by the temperature detection element, whether said electronic thermometer has been inserted in the measurement target, prediction value derivation means for performing a deriving process involving deriving a plurality of prediction values from actual measurement values in accordance with a plurality of prediction equations, starting means for starting the deriving process performed by the prediction value derivation means when the determination means determines that said electronic thermometer has been inserted in the measurement target, selection means for selecting, after elapse of a predetermined period of time from the time at which the determination means determines that said electronic thermometer has been inserted in the measurement target, a prediction equation, which minimizes a temporal change of prediction value, among the plurality of prediction equations, and display output means for displaying a prediction value result on the basis of the selected prediction equation.