PURPOSE: To insert an already wiring finished connection case body between case bodies, which are connected with each other, to connect the case bodies with each other and to improve the workability of the wiring of a cable between the case bodies.

CONSTITUTION: A cable 3 for connecting a first case body 1a with a second case body 2a is already finished wiring between the case body 1a, which is connected with the cable, and the case body 2a, which is made a cable connection, and a connection case body 10a with input/output positions 4b and 5b limited centering around the case body 10a is inserted between the case bodies 1a and 2a. In the case where the case bodies 1a an 2a are now made a cable connection with each other, the work of the wiring of the cable between the case bodies can be simply executed by merely connecting an input/output connector 6a at an input/output position 4a with an input/output connector 6b at the position 4b and an input/output connector 7a at an input/output position 5a with an input/output connector 7b at the position 5b because the input/output pisitions 4b and 5b are limited centering around the case body 10a.