A mandatory hooking/locking device for an elevating footboard of a pull-up exercise machine includes a touch-pressing rod disposed at stepping positions with respect to an exerciser's two soles separately and acted by a rotary plate and a torsion spring to achieve a lifting effect to freely penetrate and slightly elevate from an end surface of the elevating footboard, and a hooking portion disposed at the bottom end of the rotary plate being provided for hooking to a corresponsive latch column of an inwardly extending section in the floor affixing front stand, so that the hooking portion of the rotary plate can be separated from the latch column only if the two touch-pressing rods are stepped and pressed down simultaneously, so that the elevating footboard performs the expected ascending and descending motions to ensure the safety of use.