1. A data retrieval device, comprising: a storage part that stores data; a retrieval item divider that divides retrieval conditions related to a predetermined retrieval item into a plurality of retrieval condition classes; a retrieval part that respectively sorts the data stored in the storage part into the plurality of retrieval condition classes formed by the retrieval item divider by searching for data that respectively satisfies the retrieval conditions corresponding to each retrieval condition class; an output part that respectively associates the plurality of retrieval condition classes with information related to the data sorted into the retrieval condition classes by the retrieval part, and outputs the same; an input part that receives commands input from a user; a class unit modifier that further divides a selected retrieval condition class into a plurality of retrieval condition classes when a command selecting one of the retrieval condition classes from among the plurality of retrieval condition classes output by the output part is input into the input part; and a retrieval controller that controls the retrieval part to respectively sort the data that was sorted into the retrieval condition class selected by the input part into the retrieval condition classes formed by the class unit modifier.