A breach lock mechanism in a tire vulcanizing machine for clamping upper and lower metal molds under pressure is improved so as to reduce a number or parts, simplify a structure and lower a cost. The tire vulcanizing machine comprises a lower metal mold supported on a base, an upper metal mold supported from a bolster and adapted to be placed on the lower metal mold, an upper ring rotatably fitted around an outer circumferential portion of the bolster and having claws at its lower end, a lower ring supported from the base in a vertically movable manner and having claws at its upper end, first drive means for rotating the upper ring, and second drive means for vertically moving the lower ring. The claws of the upper ring and the claws of the upper ring are adapted to be engaged with or disengaged from each other as a result of rotation of the upper ring, and the upper and lower metal molds are pressurized by lowering the lower ring when the claws of the upper ring and the claws of the lower ring are engaged with each other. Preferably, either or both of the claws of the upper ring and the claws of the lower ring are formed at a plurality of levels so that the engaging position between the upper and lower rings can be adjusted depending upon a total height of the upper and lower metal molds.