Abstract: A rotation detecting apparatus disposed on the outer periphery of a compressor including an airtight casing containing a rotor. The rotation detecting apparatus is constituted by plural magnetism detecting elements attached to the outer periphery of the airtight casing of the compressor in correspondence with a rotational orbit of a magnet disposed on the rotor within the airtight casing, such plural magnetism detecting elements each having a core made up of at least one amorphous alloy wire and a coil wound around the outer periphery of the core.