Provided is a long-wave infrared detecting element including a magnetic field generator configured to generate a magnetic field, a substrate provided on the magnetic field generator, a magnetic-electric converter that is spaced apart from the substrate and configured to generate an electrical signal based on the magnetic field generated by the magnetic field generator, and an support unit that is provided on the substrate and supports the magnetic-electric converter in a state in which the magnetic-electric converter is spaced apart from the substrate, the support unit being configured to generate heat by absorbing incident infrared radiation, wherein the electrical signal changes corresponding to temperature changes of the magnetic-electric converter based on the incident infrared radiation directly absorbed in the magnetic-electric converter and temperature changes of the magnetic-electric converter based on the incident infrared radiation absorbed in the support unit.