Pressure sensor that mitigates zero drop phenomena

A pressure sensor fixed to a body formed with a flow path, comprising:

• a bottomed cylindrical sensor module having inside a pressure receiving chamber communicating with the flow path and including a diaphragm in contact with the pressure receiving chamber;
• a pressure detecting element fixed to the diaphragm for outputting a strain of the diaphragm as a pressure;
• a base ring disposed on an outer peripheral side of the sensor module and fixed at an outer edge of an open side end portion of the sensor module;
• a hermetic member fixed to the base ring for forming a sealed vacuum chamber opposite to the pressure receiving chamber across the diaphragm;
• a gasket sandwiched between the base ring and the body;
• and
• a pressing flange for pressing and fixing the base ring to the body through the gasket, the pressing flange being configured to apply a pressing force to the base ring from an outside to the body.