CONNECTOR CONNECTION STRUCTURE

To allow an electronic control unit to be replaced with good work efficiency and prevent foreign matter from entering a casing during maintenance work, the connector connection structure includes an internal connector positioned inside a casing, an external connector positioned outside the casing and an electronic control unit electrically connected between the external connector and the electronic control unit wherein the electronic control unit includes a main part that opposes an opening formed in the casing when the internal connector is connected thereto, and a first conductive connection portion and a second conductive connection portion provided on either end of the main part and configured to be connected to the internal connector and the external connector respectively, and a first seal member is provided on an outer periphery of the main part, the first seal member closing the opening when the external connector is not connected to the electronic control unit and the internal connector is connected to the electronic control unit.