  In transforming from Schwarzschild to Euclidean Rindler coordinates the
Schwarzschild time transforms to a periodic angle. As is well-known, this
allows one to introduce the Hawking temperature and is an origin of black hole
thermodynamics. On the other hand, according to quantum mechanics this angle is
conjugate to the $z$ component of the angular momentum. From the commutation
relation and quantization condition for the angular momentum component it is
found that the area of the horizon of a Schwarzschild black hole is quantized
with the quantum $\Delta A = 8\pi l_P^{2}$. It is shown that this conclusion is
also valid for a generic Kerr-Newman black hole.
