PURPOSE: To prevent generation of excess speed at a down slope by enabling the position on front wheel to be adjusted up and down.

CONSTITUTION: Angle θ is the angle between the line, connecting the front wheel and the rear wheel, and the horizontal plane. To attain the condition of θ=0, an upper pipe 7 is pulled up while the shaft of the front wheel 3 is pushed down by foot. When it is pushed lowermost, a bolt 4 is applied through a bolt hole 6 and a hole of a front pipe 8 and fixed with a nut 5. To accomplish angle θ, θ=θ, the upper pipe 7 is held by one hand while the handle 9 is pulled with another hand, and when the handle 9 is pulled up uppermost, the bolt 4 is penetrated to fix the front pipe 8 with the nut 5.