PURPOSE: To shorten the interruption time of light, by moving a single core connector in the same direction with a small sleeve at the time of moving the small sleeve to the single core connector on one side.

CONSTITUTION: The small sleeve 4 which connects two single core connectors 1 and 2 to be connected by being fitted in the connectors 1 and 2 is moved to the single core connector 1 side on one side, and after that, the connector is switched to another single core connector 3 by moving either single connector 1. In such a single core connector switching method, the single core connector 1 is moved in the same direction with the sleeve 4 at the time of moving the small sleeve 4 to the single core connector on one side. In such a way, the switching work of the single core connector can be simplified, thereby, it is performed rapidly and smoothly.