A rotation angle sensor includes a rotation shaft, a yoke which is made from a magnetic permeable material and includes a first disk portion, a second disk portion and a connection portion magnetically connecting the first disk portion and the second disk portion, the first disk portion and the second disk portion being provided on the rotation shaft in an axial direction of the rotation shaft separately, a first permanent magnet and a second permanent magnet, each having a disk shape which has a uniform plate thickness in a circumferential direction thereof, and which are provided on a first face of the first disk portion and a second face of the second disk portion respectively, the first face being opposed to the second face, a magnetic field detection section which is provided between the first permanent magnet and the second permanent magnet, and generates an output signal in response to an intensity of a magnetic field formed by the first permanent magnet and the second permanent magnet during a rotation of the rotation shaft. The first permanent magnet and the second permanent magnet are inclined with respect to a direction perpendicular to the axial direction of the rotation shaft so that a distance of a line passing through the magnetic field detection section and connecting the first disk portion and the second disc portion in the axis direction of the rotation shaft is gradually changed in accordance to the rotation of the shaft.