A vehicle seat includes an internal support member for supporting a seat occupant. The internal support member includes a main body in plate or sheet form positioned within a seat cushion frame and first and second mounting portions engaged by first and second cross members of the seat cushion frame. A pressure sensor is mounted on a part of an upper surface of the internal support member which is closer to the first cross member than the second cross member. The main body of the internal support member is formed with a pair of openings positioned on either side of a central longitudinal line. A sensor mounting portion supporting the pressure sensor is defined between mutually adjoining edges of the openings. The first mounting portion includes a central first mounting piece which is positioned laterally centrally and has a greater width than the sensor mounting portion.