We studied the line-of-sight (LOS) velocity field at the photospheric and chromospheric levels in the $H_{\alpha}$-loops in the course of the development of the bright flare. The spectra and filtergrams were acquired with the solar telescope ATsU-26 at the Terskol Peak Observatory. Time variations of the LOS velocities at loop tops and bases were compared to the $H_{\alpha}$ and hard X-ray fluctuations. The intensity variations and $H_{\alpha}$-filtergrams are evidence that elementary X-ray spikes are associated with consecutive disturbances of $H_{\alpha}$-loops in the arcade. The $H_{\alpha}$ intensities and velocities at the loop bases are much higher than at the tops. Different mechanisms can be efficient at the early stages of elementary X-ray spikes and at their maxima: ascent of photospheric matter at loop bases was recorded only when the $H_{\alpha}$ and hard X-ray intensities were minimum, and the intensity maxima were accompanied by descending motions of the photospheric plasma.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html