Аннотация:The Fourier analysis of the observed velocity field of ionized gas in the inner 1.5 pc of the Galactic center (obtained by Roberts and Goss, 1993) is made. As follows from the analysis, the observed field of residual velocities is dominated by the second Fourier harmonic. This fact can be treated as a consequence of the presence of an one-armed density wave with the density maximum along the Northern Arm plus Western Arc structure. The integrity of this structure is proved on the base of the continuous behaviour of the phase of the second harmonic in the whole region.