We have investigated the dependence of the spontaneous dynamics of the magnetic domain wall in ferromagnetic nanowires on the initial position of the domain wall without any external field. Using micromagnetic simulations, we have observed in detail a spontaneous magnetic domain wall motion for various wire widths and thicknesses. We have found that the average speed of the spontaneous domain wall motion significantly depends on the wire width and thickness, as well as the starting position of the domain wall motion. We conclude that the spontaneous magnetic domain wall motion should be considered very carefully in practical design of spintronic devices based on magnetic domain wall motion.