PURPOSE: To remarkably shorten the maintenance and inspection time of a meter, by making a liquid in the meter dischargeable to a common header, and applying the calibrating pressure to the common header and making the calibration of the meter possible by operating a cutoff valve of a connecting pipe, when calibrating the meter.

CONSTITUTION: A header 12 whose purpose is to execute pressing and drain treatment is installed to the inside of a meter panel 1, they are connected to a meter 2 by a test line 13, and a test valve 14 is installed to the connecting part with the header 12. Stop valves 15, 16 are provided on the outlet and the inlet of the header 12, respectively, the valve 15 is always closed, in the calibrating time, and the valve 16 is reverse to said valve. The tip of a tubing 8 of a calibrating device 7, and a quick joint 17 installed to the inside of the meter panel 1 can be connected by one-touch. When calibrating, it is executed by connecting the tubing 8 and the joint 17, operating the valves 15, 16, closing an inlet valve 9, and thereafter, opening the test valve 14, and applying the pressure to the meter.