1. An information medium recognition device for recognizing a handwritten information medium input by performing an online input operation, the information medium recognition device comprising: input means for receiving the information medium online and for outputting an information signal representing the received information medium; detection means for detecting a spectral intensity of a cosine wave component of the information medium and a spectral intensity of a sine wave processing on the information signal received from the input means; conversion means for receiving values of the spectral intensities of the cosine and sine wave components of the information medium, which are detected by the detection means, converting the value of the spectral intensity of the cosine wave component into one of a plurality of first fuzzy sets based on first membership functions by performing a fuzzy inference process thereon, and converting the value of the spectral intensity of the sine wave component into one of a plurality of second fuzzy sets based on second membership functions by performing a fuzzy inference process thereon, wherein the first membership functions are high-resolution type membership functions and are different from the second membership functions and the number of the first fuzzy sets is larger than the number of the second fuzzy sets; and judgment means for judging whether or not the information medium is genuine from the combination of the first and second fuzzy sets into which values of the spectral intensities of the cosine and sine wave components are, respectively, converted by the conversion means.