To obtain a measuring apparatus by which a pressure can be measured precisely even when the pressure is changed suddenly by a method wherein a second pressure-measuring pipe in which an orifice is installed in the middle of a water-filled water tank into which the outer end of a first pressure- measuring pipe, one end of which is the pressure detection end of a gas, is inserted from a bottom plate is provided and a pressure verification pipe in which a solenoid valve is installed is provided.

A valve 90 is closed, a hand valve 25 is opened, steam in a steam-turbine evacuation chamber 10 flows into a water tank 80, and a pressure- measuring pipe 20 is filled with the steam. A pressure at a pressure detection end 15 is transmitted to a pressure gage 40 via water inside a measuring pipe 70, and a pressure inside the evacuation chamber 10 is measured by the pressure gage 40. When the pressure inside the evacuation chamber 10 rises suddenly, the pressure is transmitted to the tank 80 so as to be transmitted to the pressure gage 40 via the water inside the measuring pipe 70. As a result, although an orifice 30 is installed, the responsivity of the pressure gage 40 becomes good.