A box includes a first cover and a second cover have engaging mechanisms which engage the one end of the first cover to the one end of the second cover, and have retaining mechanisms which retain the other end of the first cover to the other end of the second cover. The first cover and the second cover are fit to each other in a normal state when the engaging mechanisms are engaged with each other and the retaining mechanisms are retained normally. When an engagement between the engaging mechanisms is in an abnormal state, a projection abuts against at least the other of the one end of the first cover and the one end of the second cover so that a gap is formed and the interior component housed in the internal space can be seen through the gap.