Abstract: In a state estimating apparatus, an input space quantization section quantizes an input space according to a required precision of output data. A storage section calculates and stores the number of times of occurrence of output data corresponding to each input event in the quantized input space, the mean values of the output data, and the change amounts of the output data. A neighborhood definition section calculates an input space neighborhood satisfying the required precision of the output. A similar case extraction section zooms up the predetermined neighborhood of the input space to the predetermined degree and extracts input case similar to the neighborhood from input case in the input space. A similarity determination section determines the similarity between the new input event and the extracted similar input cases on the basis of the degree of zooming.