A pressure detector includes a first board with a first pressure inlet, a first groove, and a first board electrode; a second board with a second pressure inlet, a second groove, and a second board electrode; and a sensing unit arranged therebetween with a diaphragm. The first groove is in communication with the first pressure inlet so as to prevent the formation of a closed space between the first board and the diaphragm when they contact with each other. The second groove is in communication with the second pressure inlet so as to prevent the formation of a closed space between the second board and the diaphragm when they contact each other.