A controller for a rotary electric machine may include: at least one memory that stores a temperature prediction data in which a relationship among a rotational speed of a rotary electric machine, a torque information of the rotary electric machine, a temperature of the rotary electric machine at a reference time point, and a temperature of the rotary electric machine after an estimation calculation period elapses from the reference time point, and at least one processor that, at every estimation calculation period, sets the last calculation time before the estimation calculation period as the reference time point, and, by referring to the temperature prediction data, calculates an estimation value of temperature of the rotary electric machine after the estimation calculation period elapses from the last calculation time.