An resonant pressure sensor, includes: a housing; a housing-fixed portion that is fixed to the housing; a substrate that includes a substrate-fixed portion that is fixed to the housing-fixed portion and a substrate-separated portion that is separated from the housing-fixed portion and extends from the substrate-fixed portion; a first resonator that is disposed in the substrate-separated portion and that detects a change of a resonance frequency based on a strain in the substrate caused by static pressure applied by the pressure-receiving fluid; and a processor. A pressure-receiving fluid is interposed in a gap between the housing-fixed portion and the substrate and envelops the substrate. The processor measures the static pressure based on the detected change of the resonance frequency.

A pressure gauge includes: an outer container defining an outer chamber set to a reference pressure (Pr); an inner container disposed in the outer container; and a tube setting the inside of a first inner chamber of the inner container to a measurement pressure (Px). The inner container includes: a cylindrical rigid wall portion; first and second pressure receiving plates that displace due to a differential pressure between the reference pressure and the measurement pressure; a bellows partitioning the inner container into the first inner chamber and a second inner chamber; and a pressure detection element disposed in the second inner chamber and detecting the measurement pressure based on the displacements of the first and the second pressure receiving plates. The outer chamber and the second inner chamber are set to the reference pressure of a high vacuum that is lower than a lower limit of the measurement pressure.