PURPOSE: To inspect many electronic devices in a vehicle by a diagnosing unit without reaction of the devices and leakage of a signal.

CONSTITUTION: The apparatus for collecting diagnostic data of many electronic devices 6.1 to 6.n in a vehicle comprises signal line selectors 4A, 4B capable of being remotely controlling in a plug-in connecting module 4 spatially separately from a diagnosing unit 1. The selector has a switching connector 4A for selecting a diagnostic channel and a controller 4B. A connecting case 5 fixed to the vehicle is connected to the devices 6.1 to 6.n via data leads 7.1 to 7.n. The module 4 can be plug-in connected to the case 5 via contactors 4.1 to 4.n ad 5.1 to 5.n.