To provide a connector connection structure, where whether the connection part of an FPC is appropriately inserted in a connector for FPC is surely judged without having to sensation depend on vision or sensors, while defective inset of the FPC is prevented for stable quality having no defective contact.

A lock member 3 is rotated from a second position P2 to a first position P1, relative to a connector connection part 12 of an FPC1 inserted in an insert hole 22 of a connector main body 21. It is judged that the connector connection part 12 is not inserted properly in the insert hole 22 if a protruding part 33 of the lock member 3 hits a protruding part 122 provided on both sides in widthwise direction of the connector connection part 12. If the protruding part 33 of the lock member 3 does not hit the protruding part 122 of the connector connection part 12 but engages, the connector connection part 12 is judged to be inserted properly into the insert hole 22.