Included are a bottom portion having a traveling portion, a body portion having a first pillar portion and a second pillar portion extending in a vertical direction, respectively, from one end and another end in a horizontal direction of the bottom portion, and a top portion including one end connected to an end of the first pillar portion opposite to the bottom portion and including another end connected to an end of the second pillar portion opposite to the bottom portion, an article storage portion that forms an opening with the first pillar portion, the second pillar portion, the top portion, and the bottom portion in such a way that the opening penetrates the body portion, and fixing portions provided in the first and second pillar portions to sandwich the opening and pair up with each other, for fixing an article storage auxiliary instrument.