To provide a joint structure of a toothed belt capable of reducing height of a step in a joint part, preventing occurrence of crack even by bending of the belt, and preventing occurrence of disorder of a core body due to cutting the core body obliquely.

In this belt formed into an endless shape by fusing a thermoplastic material by butting and pressing end parts of the belt constituted by burying a core wire into the thermoplastic material mutually in a mold, a rectangular protruding bar part forming at least one tip obliquely in the direction of width is provided in the end part 2a on one side, and a rectangular protruding bar part forming a tip having a reverse phase to that of one tip obliquely in the direction of width is provided in the end part on the other side to insert and join them so that they are mutually fitted.