  From the point of view of the R-parity breaking supersymmetric model, we
propose a scalar top (stop) search with longitudinally polarized electron (e-)
and positron(e+) beams which will soon be available at the upgraded HERA. Fully
polarized e- or e+ beams could produce the stop two times as much as
unpolarized beams, while they increase background events due to the process of
the standard model by about 30% in comparison with unpolarized ones. We show
that right-handed e+ beams at HERA is efficient to produce the stop in the
model. With 1 fb**(-1) of integrated luminosity we estimate reach in the
coupling constant lambda'(131) for masses of the stop in the range 160-400 GeV.
We can set a 95% confidence-level exclusion limit for lambda'(131) > 0.01-0.05
in the stop mass range of 240-280 GeV if no singal of the stop is observed. We
also point out that y(=Q**2/sx) distributions of e+ coming from the stop shows
the different behavior from those of the standard model.
