The present invention provides a diagnostic device that presents, to a patient, a Noise-Vocoded Speech Sound signal that is obtained by dividing at least one portion of a sound signal into a single or a plurality of frequency band signals and subjecting the frequency band signals to noise, and analyzing the content of a response recognized by the patient and the presented stimulus to diagnose a disease of the patient based on the analysis results, so that diagnosis including determining the disease of the patient and estimating a damaged site can be performed.