1. A diagnostic device comprising: a criterion change degree pattern memory that holds in store a criterion change degree pattern in association with an event-to-be-diagnosed; said criterion change degree pattern being formed of a pattern of values of the degree of change of each attribute of data, including a plurality of attributes, measured from an object being diagnosed; and change degree pattern diagnosis means for receiving a diagnostic object change degree pattern to make diagnosis of said object being diagnosed based on the received diagnostic object change degree pattern and said criterion change degree pattern stored in said criterion change degree pattern memory; said diagnostic object change degree pattern being formed of a pattern of values of the degree of change of each attribute of data, including a plurality of attributes, of said object being diagnosed, measured from said object being diagnosed, wherein said change degree pattern diagnosis means effects pattern matching between said diagnostic object change degree pattern and said criterion change degree patterns stored in said criterion change degree pattern memory to make diagnosis on an object being diagnosed based on a result of said pattern matching; said diagnostic device further comprising: attribute cardinality degree determining means for reading out the criterion change degree patterns from said criterion change degree pattern memory and for determining the degree of cardinality of each attribute in the criterion change degree pattern associated with an event-to-be-diagnosed; said attribute cardinality degree determining means sorting, from one event-to-be-diagnosed to another, the criterion change degree patterns belonging to the event in question into a pattern of interest and a training pattern; said pattern of interest being the criterion change degree pattern belonging to said event in question and said training pattern being the criterion change degree pattern belonging to remaining events; and said attribute cardinality degree determining means determining the degree of cardinality of each attribute of said criterion change degree pattern belonging to said event in question using a predetermined evaluation function.