1. An image encoding method for generating a predictive pixel value of a current picture to be coded, using pixel values of two reference pictures, and encoding the current picture using the predictive pixel value, said method comprising: a first parameter calculation step of calculating, by using a first parameter calculation unit, a first parameter corresponding to a temporal distance between the current picture and a first reference picture; a second parameter calculation step of calculating, by using a second parameter calculation unit, a second parameter corresponding to a temporal distance between the first reference picture and a second reference picture; a judgment step of judging, by using a judgment unit, whether or not a value of a third parameter calculated based on the first and second parameters is included in a predetermined range; a predictive pixel value generation step of: (i) generating, by using a predictive pixel value generation unit, a predictive pixel value of the current picture by scaling a pixel value of the first reference picture and a pixel value of the second reference picture using a weighting coefficient calculated by the first parameter and the second parameter, in a case where it is judged, in said judgment step, that the value of the third parameter is included in the predetermined range; and (ii) generating, by using a predictive pixel value generation unit, a predictive pixel value of the current picture by scaling a pixel value of the first reference picture and a pixel value of the second reference picture using a weighting coefficient of a predetermined value, in a case where it is judged, in said judgment step, that the value of the third parameter is not included in the predetermined range; and an encoding step of encoding, by using an encoding unit, the current picture using the predictive pixel value calculated in said predictive pixel value generation step.