  The influence of a quantizing magnetic field $H$ to the conductance of a
tunnel point contact in the presence of the single defect has been considered.
We demonstrate that the conductance exhibits specific magneto-quantum
oscillations, the amplitude and period of which depend on the distance between
the contact and the defect. We show that a non-monotonic dependence of the
point-contact conductance results from a superposition of two types of
oscillations: A short period oscillation arising from electron focusing by the
field $H$ and a long period oscillation of Aharonov-Bohm-type originated from
the magnetic flux passing through the closed trajectories of electrons moving
from the contact to the defect and returning back to the contact.
