To provide a pressure restrictor whose durability is excellent and by which a pressure can be regulated with good accuracy.

A pressure restrictor 4 is constituted so as to be arranged and installed in the halfway part of a pressure-guide flow passage in a pressure guide pipe 7 by which a process state is guided to a measuring instrument 5 which measures the process state in a measuring point 1. Normally, pressure- regulating bolt pins 11 provided with pressure regulating pins 11b are inserted so as to be fitted freely to first pressure-guide flow passages 4e, 4f which are formed inside the pressure restrictor 4. When the application operation or the in-line service operation of the measuring instrument 5 is performed, the pressure-regulating bolt pings 11 are replaced by shutoff plugs 21, and the operation is performed.