Patent ID: 8749229

Claim:
A rotation angle sensor comprising: a magnet that rotates about a rotation axis, the magnet having an end face perpendicular to the rotation axis and having a magnetization in a direction perpendicular to the rotation axis; and a magnetic sensor that faces the end face of the magnet and detects a magnetic field produced by the magnet, the rotation angle sensor detecting a rotation angle of the magnet based on a detection output from the magnetic sensor, wherein: the magnet includes: a plate-shaped portion including the end face of the magnet; and a ring-shaped portion that is located on a side of the plate-shaped portion farther from the end face and coupled to the plate-shaped portion, and the plate-shaped portion does not include any hollow through which the rotation axis passes, whereas the ring-shaped portion includes a hollow through which the rotation axis passes, the rotation angle sensor being configured so that on a virtual plane that is parallel to the end face of the magnet and apart from the end face by a distance equal to a distance between the end face and the magnetic sensor, the magnetic field produced by the magnet is in directions parallel to each other at a first position and a second position, the first position being a position at which the rotation axis intersects the virtual plane, the second position being different from the first position.