Surgical stapling apparatus with firing lockout mechanism

A surgical stapling apparatus comprising:

• a body portion defining a longitudinal axis having a proximal end and a distal end;
• a tool assembly supported on the distal end of the body portion, the tool assembly including an anvil assembly and a cartridge assembly, the tool assembly being movable from an unapproximated position to an approximated position,
• a drive member movably supported within the tool assembly from a retracted position to an advanced position to move the tool assembly from the unapproximated position to the approximated position, the drive member having a stop surface;
• and
• a firing lockout assembly including a latch member having a blocking member and a biasing member, the latch member being pivotally supported within the tool assembly and movable from a first position to a second position, wherein in the first position the blocking member of the latch member is aligned with the stop surface of the drive member to prevent advancement of the drive member within the tool assembly and in the second position the blocking member is misaligned with the stop surface of the drive member to permit advancement of the drive member within the tool assembly, the biasing member being positioned to urge the latch member towards the first position;
• wherein in the retracted position of the drive member, the latch member is in the first position.