the vertical direction connected to the mount 6 through a link 11 is a piston rod 10 of a cylinder 9 which is pivotally connected to the arm 8 fig4 is a longitudinal sectional view of a control lever 12 and fig5 is a plan view of the same the control lever 12 comprises a rod 13 whose upper part includes a grip portion 14 and first and second members 15 and 16 extending from both sides of it and formed as an integral part thereof thus forming spacings 17 and 18 the grip portion 14 has first upper and lower switches 19 1 and 19 2 and second upper and lower switches 20 1 and 20 2 fitted to its side faces 14a and 14b respectively the switches 19 2 and 20 2 being longitudinally spaced from the switches 19 1 and 20 1 respectively further the first and second members 15 and 16 have third upper and lower switches 21 1 and 21 2 and fourth upper and lower switches 22 1 and 22 2 fitted to the opposite faces 15a and 16a respectively the switches 21 2 and 22 2 being longitudinally spaced from the switches 21 1 and 22 1.