PURPOSE: To obtain a belt with thorns whose manufacture is easy and arrangement of the thorns can be set up freely, by forming the thorns with a roving to be wound round a square mandrel.

CONSTITUTION: A rising tip part from a fabric 17 of a roving 14 wound round a square mandrel 11 made of a reinforcing fiber such as glass or the like forming a cylindrical state of a square cross section is cut into a needlelike state and control of rising dimensions of each roving 14 is performed. Then the fabric 17 is cut off at a cut-off line C in a longitudinal direction at the central part of a peel ply 16 and the peel plies 13, 16 are removed. With this construction, the belt 22a being formed of the fabric 17 and a belt 22 with thorns where the thorns 22b are formed of the rising part from the fabric 17 of the roving 14 is completed.