A surgical stapling apparatus, comprising: a first jaw member; a cartridge configured to selectively couple to the first jaw member, the cartridge having fasteners and a platform area (427a, 427b), the cartridge defining a knife channel and an aperture; a second jaw member having an anvil with staple forming depressions; a drive member movable from a retracted to an advanced position to drive the fasteners toward the anvil, the drive member having a working end for supporting a knife, the working end being configured to move through the knife channel from a retracted to an advanced distal position for severing tissue positioned between the jaw members; and a locking mechanism comprising an actuator rotatably disposed in the aperture of the cartridge and an interlock, the actuator being movable between an initial pre-fired configuration wherein the actuator has a post and a head portion at an upper end, which rests on a platform area and is engaged with the interlock to allow distal movement of the working end, to a final post-fired configuration wherein the actuator is raised above the platform area and is disengaged from the interlock to lock out and prevent distal movement of the working end; wherein the actuator has a notch at a lower end, the actuator being biased in a downwardly direction, the head portion of the actuator having a tip 451) extending into the knife channel when the actuator is in the first pre-fired position and the interlock having an upright extension and being rotatably disposed adjacent the actuator so that the upright extension is engaged with the notch when the actuator is in the first pre-fired position, the interlock moving to a position blocking the knife channel when the actuator moves to the second post-fired position; the working end of the drive member further comprising a top flange that contacts the head portion when the drive member moves from the retracted, pre-fired position to the advanced, post-fired position thereby moving the head portion to effect disengagement of the actuator from the interlock such that the interlock is positioned inside of the translation path of the working end and the working end is locked out and unable to move distally. a first jaw member; a cartridge configured to selectively couple to the first jaw member, the cartridge having fasteners and a platform area (427a, 427b), the cartridge defining a knife channel and an aperture; a second jaw member having an anvil with staple forming depressions; a drive member movable from a retracted to an advanced position to drive the fasteners toward the anvil, the drive member having a working end for supporting a knife, the working end being configured to move through the knife channel from a retracted to an advanced distal position for severing tissue positioned between the jaw members; and a locking mechanism comprising an actuator rotatably disposed in the aperture of the cartridge and an interlock, the actuator being movable between an initial pre-fired configuration wherein the actuator has a post and a head portion at an upper end, which rests on a platform area and is engaged with the interlock to allow distal movement of the working end, to a final post-fired configuration wherein the actuator is raised above the platform area and is disengaged from the interlock to lock out and prevent distal movement of the working end; wherein the actuator has a notch at a lower end, the actuator being biased in a downwardly direction, the head portion of the actuator having a tip 451) extending into the knife channel when the actuator is in the first pre-fired position and the interlock having an upright extension and being rotatably disposed adjacent the actuator so that the upright extension is engaged with the notch when the actuator is in the first pre-fired position, the interlock moving to a position blocking the knife channel when the actuator moves to the second post-fired position; the working end of the drive member further comprising a top flange that contacts the head portion when the drive member moves from the retracted, pre-fired position to the advanced, post-fired position thereby moving the head portion to effect disengagement of the actuator from the interlock such that the interlock is positioned inside of the translation path of the working end and the working end is locked out and unable to move distally.