To provide a slide mechanism of a portable device structured to allow slide operation semiautomatically, and a portable telephone provided with the slide mechanism of the portable device, it comprises a base member 5 mounted on either one of the first casing 2 and the second casing 3, a slider 4 slidably engaged with the base member 5 and mounted on the other of the first casing 2 and the second casing 3, and a slide energizing means 6 provided between the slider 4 and the base member 5. The slide energizing means 6 is constituted of a rotary arm 7 rotatably mounted on either one of the base member 5 and the slider 4, and an energizing member 8 mounted on the other of the base member 5 and the slider 4, allowing the first casing 2 and the second casing 3 to automatically open/close from a predetermined opening/closing position by acting on the rotary arm 7 to energize the rotary arm 7 to rotate from a predetermined rotary position to both of right and left directions.