PROLEG is a famous computer program supporting attorneys in the legal inference process. However, the input of this system is expressed in Prolog, which most lawyers are not familiar with. This technical barrier is a serious problem for using PROLEG in the real legal context. A natural language interface is one of the solutions to this problem. We have developed a prototype of such an interface. This paper describes the prototype and its current performance. The prototype translates input facts into Prolog expressions following PROLEG syntax. The system consists of three main modules, (1) natural language perceiver, (2) PROLEG reasoner, and (3) inference explainer. In addition, we analyze the performance of the prototype and identify existing issues and discuss possible solutions.