Abstract: An improved extendible telephone having a main casing incorporating a receiver and an auxiliary casing incorporating a transmitter and dial keys and slidably mounted on the main casing. Guide grooves are formed in each of the slide surface of the main casing and a back plate which is fastened to the auxiliary casing. Rail members are fitted in the slide surface of the main casing. The auxiliary casing is slidable along the rail members toward and away from an extended position while being guided by the guide grooves. The rail members each has an angled lug while the back plate is formed with two spaced pairs of angled recesses. When the auxiliary casing is slid to the extended position or a contracted position, the angled lugs selectively mate with either of the two pairs of angled recesses to lock the auxiliary casing in position.