A watch whose watch case includes a case middle and a rotating bezel provided with a bezel locking system. The system includes a rotating crown secured to an arbor, the arbor being arranged inside a radial hole in the case middle. By rotating the crown, the user can screw or unscrew the arbor with respect to the hole. The arbor includes a frustoconical section which interacts with a pin mounted perpendicularly to the arbor and returned towards the arbor by a spring. Screwing the arbor into the hole will cause the frustoconical section to push the pin into a receiving space provided on the lower surface of the bezel, which locks the bezel. Unscrewing the arbor automatically releases the pin from the receiving space by the return force exerted by the spring. The crown can include a helium valve mechanism.