1. A driving action estimating device, comprising: a driver model for accelerator pedal operation and a driver model for brake pedal operation, each driver model being in the form of a Gaussian mixture model calculated by an EM algorithm, with time-series data of N types of characteristic amounts detected during travel of a vehicle as learning data, as a probability distribution of existence of the respective learning data in N dimensional spaces; characteristic amount obtaining means for obtaining at least one or more characteristic amounts from the N types excluding a certain characteristic amount x; maximum posterior probability calculating means for calculating a maximum posterior probability in the driver model for the obtained characteristic amount; and output means for outputting an estimated value of the certain characteristic amount x for the obtained characteristic amount based on the calculated maximum posterior probability.