A rotation angle detection device for detecting rotation angle of a rotating body to be measured includes magnetic detection elements which are fixed to a stator and detect magnetic flux density of a magnet which is rotated with the rotating body. The device can calculate rotation angle of the rotating body from outputs of the magnetic detection elements. The device also includes magnetic bodies having two edge portions in positions where the magnet is inserted and arranged along an area where a magnetic line of force of the magnet is formed. Gaps can be provided between one edge portion of the magnetic bodies in the direction of the rotation center axis of the magnet and one side of the magnet in the direction of the rotation center axis, and between another edge portion of the magnetic bodies in the direction of the rotation center axis of the magnet and another side of the magnet in the direction of the rotation center axis, and the magnetic detection elements are intermediated in the magnetic line of force which passes through the magnetic bodies.