A magnetic sensor device includes a first magnet and a second magnet that are disposed on mutually opposing sides of a conveyance path, and one of poles of the first magnet faces an opposite pole of the second magnet. The first magnet and the second magnet generate a cross magnetic field whose strength in a spacing direction, which is orthogonal to a conveying direction, is within a predetermined range. An AMR element is located in a magnetic field in which the strength of the cross magnetic field in the spacing direction is within a predetermined range, and detects, as change in a resistance value, change in the cross magnetic field caused by an object to be detected. A multilayer board outputs the change in the resistance value detected by the AMR element to a processing circuit.