A portable device, such as a wristwatch, has a push-button that includes an engaging portion, and the push-button is mounted on a watch sheath. A stopper is arranged on the watch sheath. The stopper is movable between a locked position in which the push-button is held at a predetermined position by engagement with the engaging portion and an unlocked position in which the operation of the push-button is allowed. A circular operating ring surrounds an hour plate mounted on the watch sheath and is rotatably mounted on the watch sheath from the front side thereof. The movement of the stopper between the locked position and the unlocked position is interlocked with the rotating operation of the operating ring.