Abstract: An auto-control pencil suitable for pen leads of different sizes comprises a pen tube; a guide tube; a push rod; a spring; a rotary head; an inner head; and an outer head. When an inner head is pressed downwards along the outer head, the presses at the front end of the inner head will reduce inwards so that one end of the pen lead resists against the opening at the front end of a push rod and moreover another end thereof is clamped by the presses so that the two ends of the pen leads are fixed. Pen leads of different sizes can be used. Thus one pen is sufficient.