We analyzed the X-ray observations of Vela X-1 obtained with the Ginga large area counter (LAC) on 1991 August 18-19. During the observations, which cover orbital phase Φorb = 0.29-0.47, we detected an intensity dip at Φorb = 0.33-0.38. The pulse amplitude of the X-ray flux was much reduced in the dip and was almost invisible in lower energy band. From the spectroscopic study, clear modulation of the iron line flux with the pulse period was observed at the half-amplitude of 10% during the dip. We also detected modulation of the iron line center energy in the data set obtained at Φorb = 0.43-0.47. These phenomena may be explained by the X-ray reprocessing in the accretion wake.