A rotation angle sensor providing excellent output characteristics is provided. The rotation angle sensor has a structure in which a ring-shaped permanent magnet provided so as to be rotatable integrally with a rotor connected to a member to be detected; magnetic flux gathering yokes surrounding the outer circumferential surface of the ring-shaped permanent magnet with a certain clearance being formed between the outer circumferential surface and the magnetic flux gathering yokes; and Hall ICs 30 arranged in gaps between the magnetic flux gathering yokes, are arranged inside a casing formed by a casing body and a cover. In the casing body, a guide tube surrounding the outer circumferential surface of the ring-shaped permanent magnet is formed with a certain clearance being formed between the outer circumferential surface and the guide tube. The guide tube is made of a material having a linear expansion coefficient smaller than that of the casing, and the magnetic flux gathering yokes are fixed to the outer circumferential surface of the guide tube.