PURPOSE: To stabilize the voltage level of a signal land (SG) by providing printed circuit board supported by a pair of guide rails and earth springs which are fixed to both end sections of the printed circuit board on the guide rail sides and slid on the guide rails.

CONSTITUTION: A pair of guide rails 13 which support a printed circuit board 12 are fitted to the top and bottom of a printed circuit board rack 11. Back panels 14 for fixing the board 12 to the rack 11 are fixed to the front end section on the right side of the board 12 with screws 15. In addition, a plurality of earth springs 16 fixed to the upper and lower both end sections of the board 12 with screws 18 through holders 17. Accordingly, the SG of the printed circuit board and printed circuit board rack can be electrically connected to each other at numerous points. Therefore, the voltage level of the SG of the printed circuit board can be stabilized, since the variation of the voltage level is quickly absorbed.