To provide a rotation angle detection device applied to detection of a rotation angle of a joint part of a machine with a joint or a turning shaft of a machine with the turning shaft, having a small size, high resolution and high resistance against an environmental change, capable of detecting an absolute angle, and improving assembleability and incorporability.

In this rotation angle detection device, the rotation angle of a joint part is detected, in a machine with the joint such as a construction machine or an industrial machine having the joint part. A magnetism generation means 28 having circumferential direction anisotropy around the rotation center is provided on either joint constituting member between a pair of mutually-rotatable joint constituting members constituting the joint part. A magnetic array sensor 29 for detecting magnetism from the magnetism generation means 28 is provided on the other joint constituting member oppositely to the axial direction of the rotation center of the magnetism generation means 28. An angle calculation means 30 for calculating the rotation angle of the magnetism generation means 28 from an output from the magnetic array sensor 29 is provided.