When the hydrogen absorbing alloy was packed in the pressure vessel, the effect of cyclic hydrogen absorption/desorption on the stress developed on the side wall of the vessel and the packing state of the packed bed of the alloy was investigated. The effect of the change in the packing state of the packed bed on the stress was also investigated. While the stress developed on the side wall of the vessel of the packed bed was not observed in the upper region of the vessel, the stress increased with the increase in the number of hydrogen absorption/desorption cycles and showed constant value in the lower region of the vessel. Also, with the increase in the number of cycles, the local packing fraction of the packed bed decreased in the upper region whereas the fraction rose to around 0.7 and then showed a constant value in the lower region. Furthermore, it was suggested that the stress becomes higher in the region with the higher local packing fraction and for the larger number of the cycles even though the fraction is the same. It was also suggested that the local packing fraction becomes a constant value after about 20 cycles of hydrogen absorption/desorption.