A magnetic sensor device, comprising: - a magnetic field generator including a first magnetic pole part forming a first magnetic pole and a second magnetic pole part forming a second magnetic pole having a reverse polarity of the first magnetic pole, and generating a cross magnetic field crossing a sheet-shaped object-to-be-detected containing a magnetic component at a position to which the object-to-be-detected is conveyed by the first magnetic pole part and the second magnetic pole part; - a magnetic resistance effect element disposed between the first magnetic pole part and a position to which the object-to-be-detected is conveyed, a resistance value of the magnetic resistance effect element changes according to a change in a component of the cross magnetic field in a conveying direction, the change generated by the object-to-be-detected being conveyed along the conveying direction in the cross magnetic field; and - a magnetic material part formed of a metal and disposed between the first magnetic pole part and the magnetic resistance effect element; wherein the magnetic resistance effect element is mounted at the magnetic material part; wherein the position of the magnetic resistance effect element in the conveying direction is a position shifted along the conveying direction from a center position of the first magnetic pole part in the conveying direction, and located between ends of the first magnetic pole part in the conveying direction, the magnetic sensor device characterized by further comprising: - a non-magnetic material part formed of a metal, extending in the conveying direction of the magnetic material part, and joined to the magnetic material part; and - a signal processor mounted at the non-magnetic material part and connected electrically to the magnetic resistance effect element. - a magnetic field generator including a first magnetic pole part forming a first magnetic pole and a second magnetic pole part forming a second magnetic pole having a reverse polarity of the first magnetic pole, and generating a cross magnetic field crossing a sheet-shaped object-to-be-detected containing a magnetic component at a position to which the object-to-be-detected is conveyed by the first magnetic pole part and the second magnetic pole part; - a magnetic resistance effect element disposed between the first magnetic pole part and a position to which the object-to-be-detected is conveyed, a resistance value of the magnetic resistance effect element changes according to a change in a component of the cross magnetic field in a conveying direction, the change generated by the object-to-be-detected being conveyed along the conveying direction in the cross magnetic field; and - a magnetic material part formed of a metal and disposed between the first magnetic pole part and the magnetic resistance effect element; wherein the magnetic resistance effect element is mounted at the magnetic material part; - a non-magnetic material part formed of a metal, extending in the conveying direction of the magnetic material part, and joined to the magnetic material part; and - a signal processor mounted at the non-magnetic material part and connected electrically to the magnetic resistance effect element.