There is provided a device for preventing the jutting-out of the ladder of a ladder truck, wherein when the extending and contracting operation of an extensible ladder is completed and a ladder extending and contracting changeover valve is returned to its neutral position, locking levers are automatically turned to their locking position with respect to several stage ladders required to be prevented from jutting out, thereby providing for prevention of jutting-out, whereas at the time of extension and contraction of the extensible ladder said locking levers are turned to their retracted position to enable the extension and contraction to be effected without hindrance.