A magnetic sensor device that includes an annular magnetic body, a coil wound around the magnetic body, the coil configured to apply a magnetic field that rotates 360 degrees by a half way point in a peripheral direction of the magnetic body, and a magnetoresistance effect element arranged at a center of the annular magnetic body and including a fixed layer having a magnetization direction fixed in a direction of the magnetic field to be measured. The magnetic body includes a tapered portion located at a position where a line passing through the center of the magnetic body and extending in a shorter-axis direction intersects the magnetic body, the tapered portion having a narrowed portion narrowed down toward the magnetoresistance effect element, and having dumbbell-shaped inner and outer peripheries, and the narrowed portion having a width reduced toward the magnetoresistance effect element.