Provided is a pressure sensor for detecting the pressure of liquid flowing in a main flow path, including: an introduction flow path to which liquid is introduced from the main flow path; a pressure detection element having a pressure receiving surface and for detecting the pressure of liquid received by the pressure receiving surface in the introduction flow path; a diaphragm provided in a downstream-side end part of the introduction flow path and for transferring the pressure of the liquid to the pressure receiving surface while isolating a contact between the liquid in the introduction flow path and the pressure receiving surface; and a leak sensor for detecting a leakage of liquid into an internal space in communication with the pressure receiving surface.