A magnetic field detection device including a magnetic body (magnetic flux guide) provided for adjusting a magnetic field to be applied to a magneto-resistance element. A shape of an on-substrate magnetic body in plan view is a tapered shape on one end portion side and a substantially funnel shape on another end portion side opposite the one end portion, the another end portion being larger in width than the one end portion, and a magneto-resistance element is disposed in front of an output-side end portion. In the on-substrate magnetic body, a contour of a tapered portion is not linear like a funnel, but has a curved shape in which a first curved portion protruding outward with a gentle curvature and a second curved portion protruding inward with a curvature similar to that of the first curved portion are continuously formed.