A conventional rotation angle detection device is formed of a first magnet spaced apart from a rotation axis of a rotary body, a second magnet positioned oppositely to the first magnet relative to the rotation axis, a first yoke connecting N-poles of the first magnet and the second magnet, a second yoke connecting S-poles of the first magnet and the second magnet, and a magnetism detection element positioned on the rotation axis. For example, the first yoke and the second yoke are fixed to the rotary body, while the magnetism detection element is fixed to a support body. The rotation angle detection device detects a rotation angle of the rotary body based on an output of the magnetism detection element, which varies with a rotation of the rotary body relative to the support body.
A rotation angle detection device disclosed in JP-A-2003-185471 has two stator core pieces, which sandwich a magnetism detection element, to linearize magnetic flux passing near the magnetism detection element. According to this rotation angle detection device, the magnetic flux passing near the magnetism detection element bends when the stator core pieces are removed. When the magnetic flux passing near the magnetism detection element bend, a detection result changes in response to a positional deviation between the rotary body and the support body even in a case that the rotation angle of the rotary body is the same.