Sensor device

1. A sensor device comprising:

a partial assembly constituted by selectively mounting to a holder a part that is a driven wheel and that is a magnetism collection member, the magnetism collection member being configured to induce magnetic flux that matches torsion of a shaft as a detection target, and the driven wheel being configured to rotate in conjunction with rotation of the shaft;

a circuit board provided with a detector configured to detect a rotational angle of the driven wheel and the magnetic flux induced by the magnetism collection member in accordance with the part mounted to the holder; and

a sensor housing that is penetrated by the shaft and that houses the partial assembly and the circuit board, wherein:

the partial assembly includes a holding member that holds the driven wheel on the holder,

the sensor housing is configured to suppress entry of dust or a liquid into the sensor housing, and

the partial assembly does not have a function as the sensor housing and the holder does not constitute a part of the sensor housing.

2. The sensor device according to claim 1 , wherein the holder includes an engagement portion, the partial assembly being held inside the sensor housing with the engagement portion engaged with a portion of the sensor housing.

3. The sensor device according to claim 1 , wherein the holding member is mounted to the holder so as to cover the driven wheel.

4. The sensor device according to claim 1 , wherein the sensor housing includes a cover that closes an opening portion that opens toward a direction that intersects with an axis of the shaft, the cover being provided on an assumption that the sensor housing includes a housing chamber that houses the partial assembly and the circuit board via the opening portion.

5. The sensor device according to claim 1 , wherein the shaft is rotated in conjunction with an operation of a steering wheel.