PURPOSE: To improve the translation accuracy by designating plural filters out of a prepared filter library in response to the document to be translated and using these filters after connecting them to each other.

CONSTITUTION: An input sentence obtained from a subject text 3 undergoes the pre-processing via a pre-editing part 4 with input of a keyboard 2. Under such conditions, a filter 5 is selected out of a filter table 7. Thus the pre- processed sentence is inputted to a translation part 8 via the filter 5. The filters can be connected to each other by the selection of a user. As a result, a document to be translated can be converted into a translatable form. Furthermore the connected filters which are frequently used are registered by the user and therefore customized. Thus it is not required to set the same connected filters at each time.