PURPOSE: To obtain an interface that can correspond to a desired transfer speed with no deterioration of the throughput and with no abnormal working by supplying a clock after converting it via a speed converting part in accordance with the designation of a handshake speed designating area set on a subroutine of a computer.

CONSTITUTION: A handshake speed designating area is secured on a subroutine set in a computer 60 of a controller 100 which controls an equipment to be controlled. A speed converting part 90 which is formed by a variable divider is controlled with the designation of a handshake speed designating area. Then a clock (1) is divided in accordance with the designation and a conversion clock (2)is supplied. An interface part 70 transfers the information at a speed corresponding to the clock (2). Thus it is possible to obtain an interface for control of measuring instruments that can correspond to a desired transfer speed with no deterioration of the throughput and with no abnormal working.