4. The output parameter estimation apparatus of claim 2, wherein the route selection means selects the routes between the introduction layer and the input layer in accordance with a proximity of the centroid to the adjacent field.
4. The output parameter estimation apparatus of claim 2, wherein the route selection means selects the routes between the introduction layer and the input layer in accordance with a proximity of the centroid to the adjacent field. 5. The output parameter estimation apparatus of claim 4, wherein the input data set is composed of a plurality of physical parameter values that are detected in an engine, an intake system, and an exhaust system while the engine is being used, wherein the output parameter value is an air/fuel ratio that is estimated as an actual air/fuel ratio in the engine, the actual air/fuel ratio being unable to be detected by an air/fuel ratio sensor installed in the exhaust system, wherein the neural network is a hierarchical neural network where the plurality of physical parameter values are inputted in the input layer and the estimated air/fuel ratio is outputted from the output layer, and wherein the field division information storage means stores information showing the plurality of fields that are generated by dividing each of at least two physical parameters that include an engine RPM and an intake air pressure into three ranges that are a low-speed range, a medium-speed range, and a high-speed range.