The present invention is intended to provide an on-demand interface device which is capable of retrieving a function corresponding in meaning to an inputted request sentence and easily executing the retrieved function. The on-demand interface device comprises a function-description database containing function-descriptive sentences for respective functional items and action scripts for realizing respective functions, retrieving means for retrieving a functional item corresponding to a requesting sentence inputted through an input means, script executing means for realizing the retrieved function by executing a corresponding script. The retrieving means can conduct the retrieval of keywords as well as the retrieval of a requesting function by determining an inner product of two sentence vectors, i.e., of a request and each of function-descriptions for respective functional items.