PURPOSE: To save recording paper by performing automatic recording of pressure by rotating the recording paper only in the time zone wherein recording is required.

CONSTITUTION: Even after the valve of a main-pressure regulator for regulating the flow rate of gas in a main pipe is closed, the differential pressure on the upstream side and on the downstream side of a secondary pressure regulator for regulating the flow rate of a minute amount of gas in a branch pipe is automatically recorded with an automatic pressure gage for detecting gas leakage 1. The pressure gage 1 is constituted of a recording pointer 9, whose tip is pushed on recording paper 10 that is rotatadly supported, a pressure changing means 15, which moves the recording pointer 9 in the direction of the diameter of the recording paper 10 in correspondence with the magnitude of the pressure to be measured, and a clock body 20, which rotates the recording paper 10 only in the limited time zone in one day.