A rear wheel drive mechanism acting as a drive force transmission mechanism provided in a vehicle is provided with a spline section provided on an outer periphery of one end of a first drive shaft acting as an output shaft, a spline hole provided on an inner periphery of a tubular engaging section of a universal joint and engaging with the spline section, and a circular clip disposed spanning the inner periphery and the outer periphery. An operating section of the clip faces a notched section provided on the tubular engaging section. The notched section is provided on a tip of the tubular engaging section and opens with respect to an axial dimension of the first drive shaft. The drive mechanism so configured simplifies the operation of mounting or removing a universal joint onto an output shaft of a vehicle.