A stapling head assembly includes a cartridge support having a proximal end, a connecting tube, a cutter pushing rod, and a lockout mechanism. The tube includes a distal end connected to the proximal end. The rod is movably set inside the tube. The mechanism is connected to the tube, and includes a pressing block and a pushing block. The pressing block is used to lock the proximal end to prevent the rod from moving before the assembly is used. The pressing block is rotatable between a first position and a second position relative to the tube. The pushing block is used to push the pressing block to rotate from the first position towards the second position. The pushing block is located at one side of the pressing block, and is movable between a third position and a fourth position relative to the tube along a longitudinal direction.
