A long-wave infrared detecting element includes a magnetic field generator configured to generate a magnetic field; a substrate on the magnetic field generator; a superparamagnetic material layer disposed to be separated from the substrate and magnetized by the magnetic field generated by the magnetic field generator; a support unit on the substrate to support the superparamagnetic material layer such that the superparamagnetic material layer separated from the substrate, such that the support unit and the superparamagnetic material layer generate heat by absorbing infrared radiation from the outside; and a magneto-electric conversion unit that generates an electrical signal proportional to both a strength of the magnetic field generated by the magnetic field generator and the magnetization of the superparamagnetic material layer.