  Parallax measurements allow distances to celestial objects to be determined.
Coupled with measurement of their position on the celestial sphere, it gives a
full three-dimensional picture of the location of the objects relative to the
observer. The distortion of the parallax value of a remote source affected by a
weak microlensing is considered. This means that the weak microlensing leads to
distortion of the distance scale. It is shown that the distortions to appear
may change strongly the parallax values in case they amount to several
microseconds of arc. In particular, at this accuracy many measured values of
the parallaxes must be negative.
