A sensor assembly configured to be included in a torque sensor including a magnetic flux output device configured to output a magnetic flux in response to torsion produced between ends of a torsion bar, the sensor assembly comprising: a magnetic sensor circuit configured to output a detection value indicating a torque applied to the torsion bar, the detection value being calculated from the magnetic flux output from the magnetic flux output device, the magnetic sensor circuit including a substrate which includes a first circuit principal surface and a second circuit principal surface; a holder holding the magnetic sensor circuit; and a injection molded case containing the holder, wherein the holder includes a first holder member including a first holder principal surface facing the first circuit principal surface of the magnetic sensor circuit, and a second holder member including a second holder principal surface facing the second circuit principal surface of the magnetic sensor circuit, the first holder member further includes a first holder side wall protruding from the first holder principal surface toward the second holder member, the magnetic sensor circuit is partially disposed in a space defined by the first holder member, the second holder member, and the first holder side wall and is thus held by the holder, characterized in that the first holder side wall is a thin plate member configured to be inclined inward and in contact with the second holder member upon being applied with pressure forces from the resin material so as to prevent intrusion of the resin material of the injection molded case into an inner space of the holder from outside the holder, and the injection molded case is made of a resin, the case being in contact with a first holder side wall outer surface of the first holder side wall. a magnetic sensor circuit configured to output a detection value indicating a torque applied to the torsion bar, the detection value being calculated from the magnetic flux output from the magnetic flux output device, the magnetic sensor circuit including a substrate which includes a first circuit principal surface and a second circuit principal surface; a holder holding the magnetic sensor circuit; and a injection molded case containing the holder, wherein the holder includes a first holder member including a first holder principal surface facing the first circuit principal surface of the magnetic sensor circuit, and a second holder member including a second holder principal surface facing the second circuit principal surface of the magnetic sensor circuit, a first holder member including a first holder principal surface facing the first circuit principal surface of the magnetic sensor circuit, and a second holder member including a second holder principal surface facing the second circuit principal surface of the magnetic sensor circuit, the first holder member further includes a first holder side wall protruding from the first holder principal surface toward the second holder member, the magnetic sensor circuit is partially disposed in a space defined by the first holder member, the second holder member, and the first holder side wall and is thus held by the holder, the first holder side wall is a thin plate member configured to be inclined inward and in contact with the second holder member upon being applied with pressure forces from the resin material so as to prevent intrusion of the resin material of the injection molded case into an inner space of the holder from outside the holder, and the injection molded case is made of a resin, the case being in contact with a first holder side wall outer surface of the first holder side wall.