A pressure sensor , comprising: a pressure detector that detects a pressure of a detection target; a housing portion that includes a housing part housing the pressure detector , a concave portion facing the housing part across an inner wall , and a through hole part formed in the inner wall and allowing the housing part and the concave portion to communicate with each other; a filter that covers the through hole part ; and a cover that is mounted on the housing portion while covering the concave portion and includes an atmospheric opening part, wherein the concave portion is formed by a bottom surface that is one surface of the inner wall , and two side surfaces that are perpendicular to the bottom surface and are opposed to each other, the cover is formed by an upper plate having a rectangular shape and two side plates having a rectangular shape that are perpendicular to the upper plate and are opposed to each other, the upper plate is arranged to face the bottom surface of the concave portion , and the two side plates are arranged between the two side surfaces of the concave portion that are opposed to each other to form a space portion surrounded by the two side plates and the two side surfaces , the housing portion includes two side walls whose surfaces are continuous with the bottom surface of the concaved portion and are positioned at sides of the housing part , characterized in that the two side walls include projecting parts projecting outward, and a part of each of the two side plates of the cover faces one of the two side walls and includes an engagement hole part with which one of the projecting parts engages. a pressure detector that detects a pressure of a detection target; a housing portion that includes a housing part housing the pressure detector , a concave portion facing the housing part across an inner wall , and a through hole part formed in the inner wall and allowing the housing part and the concave portion to communicate with each other; a filter that covers the through hole part ; and a cover that is mounted on the housing portion while covering the concave portion and includes an atmospheric opening part, wherein the concave portion is formed by a bottom surface that is one surface of the inner wall , and two side surfaces that are perpendicular to the bottom surface and are opposed to each other, the cover is formed by an upper plate having a rectangular shape and two side plates having a rectangular shape that are perpendicular to the upper plate and are opposed to each other, the upper plate is arranged to face the bottom surface of the concave portion , and the two side plates are arranged between the two side surfaces of the concave portion that are opposed to each other to form a space portion surrounded by the two side plates and the two side surfaces , the housing portion includes two side walls whose surfaces are continuous with the bottom surface of the concaved portion and are positioned at sides of the housing part , characterized in that the two side walls include projecting parts projecting outward, and a part of each of the two side plates of the cover faces one of the two side walls and includes an engagement hole part with which one of the projecting parts engages. <EOS>