A pressure sensor includes a cylindrical member configured to be attached to a body having a fluid passage, and a pressure sensor unit connected to the cylindrical member for detecting a pressure of a fluid flowing through the fluid passage, wherein the cylindrical member is made of a nickel-molybdenum-chromium alloy material or a stainless steel material, wherein the pressure sensor unit includes a sensor body closed at one end with a diaphragm and a pressure detecting element for outputting displacement of the diaphragm as pressure, and wherein the sensor body is made of a cobalt-nickel alloy material, and is connected at an opening side end portion to one end portion of the cylindrical member.