To provide a rotation angle detector with superior detection accuracy which is used in the detection of a rotation angle in steering of an automobile.

The rotation angle detector is provided with a concave part 21C which is made up by sinking the surroundings of a shaft part 22 and disposed on the upper surface of a detecting body 21, and composed so that a journalling part 25B of an upper cover 25 is prolonged up to the concave part 21C. As a result, the shaft part 22 of the detecting body 21 is journalled by the journalling part 25B over a long span, and rotational looseness between a through hole 25A and the shaft part 22 and/or rotational wobbling of a magnet 3 on the tip of the detecting body 21 due to the rotational looseness are reduced. Therefore, detection signals little in error are detected by a detecting means, and the superior detection accuracy can be obtained.