To reconstitute a switch connection route according to a change of connection of module groups.

Each of modules 86, 87, and 88 has three contacts severally. When electric power is supplied from a constant-current power supply 82 to the module 86, a switch 90 decides a contact 93 as a route contact to the module 86, and decides the rest contacts 94, 99 as branch contacts. Similarly, when electric power is supplied from the module 86 to the module 87, the switch 90 decides the contact 93 as the route contact to the module 86, the contact 95 as the route contact, and the contact 96 as the branch contact. In this pattern, the decision is conducted about the module 88, so that the contacts 97, 98 are decided as the route contact and the branch contact respectively. Therefore, a switch connection route is set in such a way to pass the modules 86, 87, and 88, and the branch contacts 98, 99 are drawn into a non-operation state by an electromechanical mechanism and the like so as to prevent the branch modules from connecting each other between electronic modules.