A rotation angle detection device includes a magnetic field generation section, a yoke, and a magnetism detection section. The magnetic field generation section has a first end portion and a second end portion. The yoke has such a tube shape that the magnetic field generation section and a rotation axis of a rotating body are located therein. The yoke has a gap at a part in a circumferential direction in a cross section perpendicular to the rotation axis. The magnetism detection section is disposed in the gap and outputs an electrical signal in accordance with a magnetic field strength in the gap. The magnetic field generation section is disposed in such a manner that a magnetic force line passing through the magnetic field generation section passes through the rotation axis regardless of the rotation angle of the rotating body and the rotation axis passes through the first end portion.