To make the measurement preparation work of a competition speedy and efficient, to prevent any competition from being affected during that competition and to prevent a connector box from unexpectedly jumping out when vertically moving it.

Concerning a connector box 3 installed in a hand hole 1 formed on a sports ground, this connector box 3 can be freely moved up and down, a balancer is attached for applying force balanced with the weight of the connector box 3 and during the competition, the connector box 3 is incorporated inside the hand hole 1 but during the measurement preparation work, it can appear out of the hand hole 1. This balancer is composed of a high pressure spring and one-to-one force is practically applied to the connector box 3.