The power assisting device includes driver with a rotary axis, a main gear, a first transmission rod, a first bevel gear, a second bevel gear, a first rotating rod, a third bevel gear, and a first driving wheel. The main gear is driven by the driver to rotate about the rotary axis. The first transmission rod extends along a direction perpendicular to the rotary axis. The first bevel gear and the second bevel gear are separately sleeved on the transmission rod. The first bevel gear is engaged with the main gear. The first rotating rod extends along a direction parallel to the rotary axis. The third bevel gear is sleeved on the first rotating rod and is engaged with the second bevel gear. The first driving wheel is coupled to the first rotating rod for assisting a wheel of a vehicle to move forward.