A surgical instrument comprising: an elongate housing having a proximal end and a distal end； a loading unit removably mountable with the distal end of the elongated housing and having a tool assembly, the loading unit having at least one lug thereon； and a handle assembly at the proximal end of the elongated housing； and a locking structure having a first position for locking movement of the loading unit and a second position for allowing movement of the loading unit, the locking structure including a locking shaft that extends through the elongated housing to the handle assembly, the locking shaft having a surface engaging the at least one lug in the first position of the locking structure and disengaging the at least one lug in the second position of the locking structure.
