1. A computer system for determining applicability of information retrieving processes, comprising: a first computer storage for storing keywords indicating necessary information for an information retrieving process; a second computer storage for storing past retrieval case data including expressions extracted from voice data associated with an operation of the information retrieving process that matches the stored keywords in the first computer storage, an identification of a document selected in the operation of the information retrieving process, an order of the selected document by the operation of the information retrieving process that represents a highest place in ranking among retrieval results of operations of the information retrieving processes performed in a certain period, and a set of retrieval keys used in the operation of the information retrieving process in which the selected document was retrieved with a best order; a third computer storage for storing the voice data associated with the operation of the information retrieving process recorded in a conversation between a customer and an operator, wherein the stored voice data includes information necessary for performing the operation of the information retrieving process; a fourth computer storage for storing retrieval history information from the operation of the information retrieving process, wherein the stored retrieval history information includes an identification of the operator performing the operation of the information retrieving process, a set of retrieval keys actually used in the operation of the information retrieving process, an identification of a document selected by the operator among retrieval results of the operation of the information retrieving process, and an order of the selected document representing a place of the selected document in ranking of retrieval results of the operation of the information retrieving process; a retrieval history information acquirer for acquiring the stored retrieval history information of the operation of the information retrieving process performed by the operator from the fourth computer storage; a voice data acquirer for acquiring the stored voice data from the third computer storage associated with the acquired stored retrieval history information; an extractor for extracting one or more expressions matching the stored keywords in the first computer storage from the acquired stored voice data; a retrieval applicability determiner for extracting the stored past retrieval case data from the second computer storage having expressions that partially correspond to the extracted one or more expressions; comparing the set of retrieval keys and the order of the selected document in the acquired stored retrieval history information to a set of best retrieval keys and a best order of the selected document in the extracted stored past retrieval case data; determining an applicability of the operation of the information retrieving process based on the comparing; and obtaining and outputting the determined applicability of the operation of the information retrieving process as an information retrieval skill of the operator.
6. The computer system according to claim 1 , further comprising: selecting the expressions from the extracted stored past retrieval case data and displaying the selected expressions to a call operator at work.