To reduce the breadth and to obtain stable operation and stabilized contact pressure.

Along with putting end vacuum valves 36 at positions right and left on a line crossing the advancing direction of a truck 35 at right angles keeping an insulation distance, a central vacuum valve 37 is put at a position in front or at the rear of the center position of both end vacuum valves 36 keeping an insulation distance with respect to both the end vacuum valves 36. Then after causing led-out conductors 16, 18 from both the end vacuum valves 36 to bulge out laterally respectively, they are extended backwards, with an insulation distance kept between the led-out conductors 16, 18. Both end and central shafts 42, 43 are interlocked by providing the central shaft 43 which moves the movable electrode 13 of the central vacuum valve 37 via the drive lever 27, in parallel to the end shafts 42 in the right and left directions which move the movable electrodes 13 of both the end vacuum valves 36 via the drive levers 27, and linking the end levers 45 fixed to the end shafts 42 to a central lever 46 fixed to the central shaft 43 by the use of a linking lever 47.