Provided is a magnetic sensor device that comprises: a bar-shaped magnet (9); a soft magnetic carrier (7a) that is disposed parallel to the magnet (9) along the longitudinal direction of the magnet (9), that has a magneto-resistance effect element (4) provided on a surface thereof opposite a surface thereof facing the magnet (9), and that extends across the length of the magnet (9) in the longitudinal direction; and a guide (14) that has a bottom portion interposed between the magnet (9) and the soft magnetic carrier (7a) and side wall portions standing upright from the bottom portion along side surfaces of the magnet (9) contacting in the longitudinal direction a surface of the magnet (9) facing the soft magnetic carrier (7a), the bottom portion and side wall portions being formed of a nonmagnetic body contacting the magnet (9) and extending in the longitudinal direction of the magnet. The magnet (9) is attracted to and held by the soft magnetic carrier (7a), with the guide (14) interposed therebetween, due to the magnetic attractive force between the magnet (9) and the soft magnetic carrier (7a).