The present invention addresses the problem of suppressing variation in the distance between a ferrimagnetic body and the side part of a conductive body cover, thereby suppressing variation in the reflection characteristic and isolation. Therefore, the present invention provides a non-reciprocal circuit element equipped with: a conductive cover provided on a substrate and covering a ferrimagnetic body provided on the substrate; the ferrimagnetic body, on at least the portion of which opposing the side part of the conductive body cover is formed a dielectric body that contacts or substantially contacts the side part of the conductive body cover; and a conductive body part provided on the substrate. Furthermore, the non-reciprocal circuit element is equipped with multiple connecting parts electrically connecting the conductive body part and each of multiple signal transmission wires on the substrate.