The motion of a curved grain boundary with a "surface triple junction" ("free surface boundary - free surface") in aluminum bicrystals is studied. The effect of the "surface triple junction" on grain boundary motion is discussed in the terms of the equilibrium of boundary and junction velocity. Boundary motion in samples with different boundary curvature revealed a strict proportionality of boundary velocity and driving force. This result corroborates the fact that in the entire investigated temperature range the "surface" triple junction does not affect the boundary motion.