Similarly, in a state in which the second positioning panel 92 abuts the end wall 32 from the back-face side of the rack 10, the back face 32A of the end wall 32, from which the second connectors 62 project, is disposed in the same plane as the mounting face 91A of the second back panel 91. Accordingly, when the back-face sides of second electronic units 40 are inserted into the rack 10, the back-face connectors 42 of the electronic units 40 are connected to the second connectors 62 and the fourth connectors 93 simultaneously. This enables the back-face connectors 42 of the electronic units 40 to be appropriately connected to the second connectors 62 and the fourth connectors 93.

(10) As illustrated in FIG. 15, the first positioning pins 81 are provided to the first positioning panel 72. In addition, the first positioning holes 22, into which the first positioning pins 81 are inserted, are formed in the first fixing portion 21 of the rack 10. Accordingly, the first positioning pins 81 are inserted into the first positioning holes 22 when the first back panel unit 70 is inserted into the rack 10, enabling the first back panel unit 70 to be positioned relative to the rack 10. This enables the ease of an operation to mount the first back panel unit 70 to the rack 10 to be improved.