In X-ray section topography of Si 220 diffraction in a multiple Bragg-Laue mode, a moiré pattern is observed when the incident beam is divided into two parts by inserting a platinum wire in the middle of the beam. The moiré pattern can be explained by the summation of two interference fringes corresponding to the two incident beams. The coherency of the X-rays from the bending-magnet beamline is estimated using the moiré pattern.