A sensing device includes: a magnetic field generating coil that generates an alternating magnetic field in a sensing-target region; a signal inducing coil in which is induced an electric signal corresponding to the alternating magnetic field generated by the magnetic field generating coil; an amplifier that amplifies a third electric signal obtained from the difference between a first electric signal induced in the signal inducing coil in a state where a sensing-target magnetic body is present in the sensing-target region and a second electric signal induced in the signal inducing coil in a state where the magnetic body is not present in the sensing-target region; and a sensing unit that senses, on the basis of the third electric signal amplified by the amplifier, the magnetic body passing through the sensing-target region by sensing a change in the magnetic field resulting from magnetization reversal of the magnetic body.