A packaging box includes a bottom case, a covering case and a buffering member. The buffering member is formed with a protruding piece protruded on the bottom plate in a direction of the side plate of the bottom case. By causing the protruding piece to abut against the side plate of the bottom case, a gap into which the side plate of the covering case can be inserted is formed with respect to the side plate of the bottom case. The bottom plate is formed with a space in which the protruding piece can be housed, at a position corresponding to the protruding piece. When the side plate of the covering case is inserted inside the side plate of the bottom case, the protruding piece of the buffering member is pressed by the side plate of the covering case and then folded to be housed in the space.