A relative rotational angular displacement detection device includes a pair of rotatable members relatively rotatable in a circumferential direction. A permanent magnet is attached to one of the rotatable members and includes magnetic poles magnetized in an axial direction of the axis of rotation and arranged to alternate in polarity in the circumferential direction. A magnetic flux inducing ring includes an annular ring body attached to the other of the rotatable members and is arranged coaxially with the axis of rotation, and a plurality of protrusions having a circumferential width smaller than a circumferential width of a magnetic pole. A magnetic detection portion is configured to detect a magnetic flux of the ring body of the magnetic flux inducing ring. The flux inducing ring is magnetized depending on a relative positions the protrusions and positions of the magnetic poles.本發明之課題在於提供一種可以簡易之構造而檢測可相對旋轉移動之一對旋轉構件之相對旋轉角度位移的相對旋轉角度位移檢測裝置等。於旋轉軸線之周向上相對旋轉之一對旋轉構件中，於一旋轉構件中設置永久磁鐵，該永久磁鐵係以於旋轉軸線之軸線方向上磁化之磁極於旋轉軸線之周向上極性交替地不同之態樣而配置者，於另一旋轉構件中設置感應圈，該感應圈包括：環狀之圈本體，其軸線配置為與旋轉軸線成同軸狀；及複數個突起部，其等以自該圈本體向上述旋轉軸線之徑方向突出且相對於上述永久磁鐵於上述旋轉軸線之軸線方向上隔開間隔而對向之態樣配置，且各自具有比上述各磁極之周向之寬度窄之周向之寬度。而且，設置磁性檢測部，該磁性檢測部係對應感應圈之各突起部與永久磁鐵之各磁極之相對位置而檢測經磁化之感應圈之圈本體之磁通量。
