PURPOSE: To reduce the cost of a magnetic sensor device by reducing the number of magnetic reluctance elements used in the device.

CONSTITUTION: Magnetic reluctance elements MR1-MRN are connected between a constant-current power source and ground GND by the number N of detecting channels, with one element being made to correspond to one channel. Voltages across both ends of the elements MR1-MRN are respectively supplied to differential amplifiers B1-BN and the differential signals of the voltages are outputted from the output side of the amplifiers B1-BN as the magnetism detecting signal of each channel. While the required number of the magnetic reluctance elements in the conventional example is twice of the number N of detecting channels, the required number of magnetic reluctance elements in this sensor is equal to the number N. Therefore, the cost of this magnetic sensor device can be reduced.