1. A learning method for use in a data processing apparatus for learning an input pattern by obtaining an internal-state value necessary for realizing a desired data conversion by performing a pattern conversion defined by the internal-state value and calculating an output pattern corresponding to the input pattern, said method comprising the steps of: (a) presenting an input pattern group of a subject to be learned for pattern conversion by a pattern presenting circuit to the data processing apparatus; (b) dividing the input pattern group of the subject to be learned into at least two sets; (c) selecting one of the divided sets; (d) presenting, by the pattern presenting circuit, the input pattern group of the selected set for pattern conversion and sequentially presenting an input pattern group belonging to all the sets presented up to the current point when internal-state value to be converged is obtained in accordance with the presentation; (e) calculating an error value, by an error calculating circuit, representing a magnitude of an inconsistency between an output pattern group outputted from a pattern converting neural network, including a multiplier, an accumulator and a threshold value processor, in accordance with the input pattern group and a teacher pattern group representing a pattern to be obtained by the output pattern group; and (f) updating an internal-state value, by an internal-state value updating circuit, in accordance with an updated quantity of the internal-state value calculated based on the error value from said error calculating circuit and obtaining an internal-state value having an error value within a specified allowance.