To solve a problem wherein a material and structure of a container, and a material and structure of a measuring detecting part are greatly limited, since the measuring detecting part contacts, directly or via a mechanical inclusion, with a vapor of a liquid of a measuring object to detect fluctuation of a pressure value, in a pressure measuring method for a gas phase part in the container for storing the liquid and the vapor of the liquid together in the conventional art.

The simple pressure measuring method of the present invention is provided without limiting the material and structure of the container, and an installation condition, since a temperature of the container for storing the liquid and the vapor of the liquid together is measured to conduct calculation by inputting it, according to a calculation expression and a calculation procedure capable of calculating an equilibrium vapor pressure of the liquid by substitution with a temperature value of the liquid of the measuring object written preliminarily in a computer and/or a storage device, each of which are one of main constitute elements of the present invention and since a calculation output value is output-value-displayed in a pressure indicator, and a device using the same is also provided in the present invention.