A sensor device whose detection target is a shaft rotatably supported on a support and formed by coupling a pair of rotation shaft members (231, 232) together by a flexible torsion shaft, and which is configured to detect a torque applied to the shaft and a rotation angle of the shaft with respect to the support, the sensor device comprising: a torque detecting portion including: a pair of soft magnetic bodies (86, 87) having facing portions (862, 872) that face each other along a rotation axis direction of the shaft; a torque detection permanent magnet configured to generate a magnetic flux in a magnetic path including the pair of soft magnetic bodies (86, 87); and a torque detection magnetic sensor (71, 72) configured to detect a magnetic field generated between the facing portions (862, 872), the magnetic field detected by the torque detection magnetic sensor (71, 72) changing based on a twisting amount of the torsion shaft; a rotation angle detecting portion including: a rotating body (76, 77) configured to rotate by meshing with an external gear configured to rotate together with the shaft; a rotation angle detection permanent magnet (78, 79) fixed to the rotating body (76, 77); and a rotation angle detection magnetic sensor (73, 74) configured to detect a magnetic field of the rotation angle detection permanent magnet (78, 79), the magnetic field detected by the rotation angle detection magnetic sensor (73, 74) changing based on the rotation angle of the shaft; a housing that houses the torque detecting portion and the rotation angle detecting portion; and a circuit board held by the housing, characterized in that the torque detection magnetic sensor (71, 72) is mounted on a first mounting portion formed in the circuit board, and the rotation angle detection magnetic sensor (73, 74) is mounted on a second mounting portion formed in the circuit board, wherein the magnetic sensors (71 to 74) are mounted on one surface of the circuit board. a torque detecting portion including: a pair of soft magnetic bodies (86, 87) having facing portions (862, 872) that face each other along a rotation axis direction of the shaft; a torque detection permanent magnet configured to generate a magnetic flux in a magnetic path including the pair of soft magnetic bodies (86, 87); and a torque detection magnetic sensor (71, 72) configured to detect a magnetic field generated between the facing portions (862, 872), the magnetic field detected by the torque detection magnetic sensor (71, 72) changing based on a twisting amount of the torsion shaft; a pair of soft magnetic bodies (86, 87) having facing portions (862, 872) that face each other along a rotation axis direction of the shaft; a torque detection permanent magnet configured to generate a magnetic flux in a magnetic path including the pair of soft magnetic bodies (86, 87); and a torque detection magnetic sensor (71, 72) configured to detect a magnetic field generated between the facing portions (862, 872), the magnetic field detected by the torque detection magnetic sensor (71, 72) changing based on a twisting amount of the torsion shaft; a rotation angle detecting portion including: a rotating body (76, 77) configured to rotate by meshing with an external gear configured to rotate together with the shaft; a rotation angle detection permanent magnet (78, 79) fixed to the rotating body (76, 77); and a rotation angle detection magnetic sensor (73, 74) configured to detect a magnetic field of the rotation angle detection permanent magnet (78, 79), the magnetic field detected by the rotation angle detection magnetic sensor (73, 74) changing based on the rotation angle of the shaft; a rotating body (76, 77) configured to rotate by meshing with an external gear configured to rotate together with the shaft; a rotation angle detection permanent magnet (78, 79) fixed to the rotating body (76, 77); and a rotation angle detection magnetic sensor (73, 74) configured to detect a magnetic field of the rotation angle detection permanent magnet (78, 79), the magnetic field detected by the rotation angle detection magnetic sensor (73, 74) changing based on the rotation angle of the shaft; a housing that houses the torque detecting portion and the rotation angle detecting portion; and a circuit board held by the housing, characterized in that the torque detection magnetic sensor (71, 72) is mounted on a first mounting portion formed in the circuit board, and the rotation angle detection magnetic sensor (73, 74) is mounted on a second mounting portion formed in the circuit board, wherein the magnetic sensors (71 to 74) are mounted on one surface of the circuit board.