PURPOSE: To smooth the behavior of a sprocket in the inclusion and release in and from a rubber crawler by providing semicircular projections longitudinally arranged on a rubber crawler and meshing holes of a sprocket meshing with the projections and having curved surfaces at both sides and a specified opening angle in the central interval portion between both curved surfaces.

CONSTITUTION: The outer peripheral edge 16 of a driving projection 13 formed integrally with the center of a core bar 11 has an arc of radius R equal to a half of the width W of a blade 12 of the core bar 11. A meshing hole 30 of a sprocket 20 has arcs 31, 32 of radius nearly equal to that of the outer periphery of the projection on both sides and a horizontal portion 33 of about several mm length on the bottom. The opening angle of the meshing hole 30 is 50-70 degrees. In the rotation of the sprocket 20, the outer peripheral edge 16 of the projection 13 abuts against the right side arc 31 of the meshing hole 30. The horizontal portion 33 gives the degree of freedom to the movement of the projection 13. Thus, the meshing hole 30 of the sprocket 20 makes surface contact with the projection so that both hole and projection mesh smoothly with each other.