A diagnostic apparatus includes an acquiring unit that acquires sound information; a first analysis unit that performs a frequency analysis of the sound information and generates frequency analysis result data representing a temporal change in an intensity distribution for each frequency; a specifying unit that specifies a frequency of an abnormal sound in the frequency analysis result data; a second analysis unit that analyzes a frequency component of the specified frequency of the abnormal sound; and an extracting unit that extracts period information of the abnormal sound from an analysis result acquired by the second analysis unit.