Deadlock is one of the most serious problems in concurrent programming.
Recently, Kobayashi proposed a static type system for a process calculus which ensures that communication over some special channels never causes deadlock. However, since the class of such channels was fixed ad hoc by the type system, the deadlock-free fragment of the calculus was limited and the essence of the type system was not so clear. In this paper, we generalize his type system in order to extend the deadlock-free part of his calculus. It is automatically checked by the type system that the usage does not cause deadlock and that the channel is actually used along the specification. As a result, the deadlock-freedom property is treated more uniformly and guaranteed more extensively.