PURPOSE: To store a cover plate so as to prevent the cover plate from opening/ closing an upper surface opening part of the case, in which an electric connection unit is mounted on the inside, and from interfering at the time of using a device.

CONSTITUTION: A first storage part 9 for storing a cover plate 4 in a vertical condition and a second storage part 10 for mounting an electric connection unit 2 are parallelly arranged in a surface direction, in a case 3 having opening on its upper surface. A device is formed by providing an operating mechanism actuated alternately in a first position of receiving a lower edge of the cover plate 4 in its vertical condition and further protruding an upper edge of the cover plate 4 a little from an upper surface of the case 3 in each pressing operation and a second position sunk from the upper surface of the case 3, in a lower part of the case 3 opposed to the first storage part 9.