Abstract: An adjustable headrest is disclosed in which a slider forming a headrest is slidably inserted into a hollow open ended casing or a space formed between left and right holding walls, or a sliding casing formed as a headrest is slidably fitted to the outside of a support fixed at the back of the seat. Disposed at suitable places between the casing and the slider are a sliding guide mechanism for the slider and engagement means for fixing the slider at the desired position in order to effect adjustment. A sliding guide mechanism permits the headrest to readily move telescopingly out of the casing. In particular, when the device of the present invention is used in conjunction with the headrest of a car seat, such headrest may be positioned so as to be generally always in contact with the head of a driver.