The invention discloses a balanced differential-type metal detection sensor and an insulating paper detection device, which relate to the technical field of metal detection devices. The sensor comprises a closed rectangular coil assembly, a sine excitation module, a differential amplifier module, a signal processing module, an A/D processing module and a data processing module, wherein the closed rectangular coil assembly comprises two receiving coils with the same structure and a transmitting coil; the two receiving coils are symmetrically arranged at two sides of the transmitting coil; the signal output end of the sine excitation module is connected with the transmitting coil; the two receiving coils are respectively connected with two input ends of the differential amplifier module; and the output end of the differential amplifier module is connected with the input end of the data processing module sequentially through the signal processing module and the A/D processing module. The sensor has high sensitivity and stability, and when the sensor is applied to the detection device, the detection device can acquire high detection precision.