FASTBUS Processor Interface (FPI), a high-speed interface which connects a FASTBUS cable segment to a VAX-family computer, has been developed at KEK in collaboration with DEC. The FPI overview, FPI implementation and benchmark results are discussed. In particular, it has been shown that FPI can transfer a 32-bit word every 200 nsec in the FASTBUS pipeline transfer mode. FPI conforms to the Nov. '82 FASTBUS specifications, and is supported by the FASTBUS Standard Routines.