To provide a measuring instrument in which a pressure in a wide range from normal pressure up to 10-2 Pa can be measured by one pressure gage.

A very small vibrator 1 which is manufactured by a silicon process is vibrated near a resonance frequency by an exciter 4, and a change in the vibrating state of the vibrator 1 due to a change in a pressure around the vibrator 1 is detected by a detector 5 which has a piezoelectric or electrostrictive characteristic. The vibrating state of the vibrator 1 is measured as a change in the phase of a vibration frequency, a change in its amplitude or a change in a mechanical quality factor. As a result, inversely, a pressure value (a vacuum) around the vibrator 1 can be known on the basis of its detection value. In addition, as a means to detect a change in the vibrating state of the vibrator 1, an optical lever and a light-wave interferometer are used.