The present invention relates to a surgical stapler comprising: a support base； a trigger； a handle； a retaining pin operatively connected to and extending distally from a support base, the support base being operable in the surgical stapler to cause the stapler to position staples near tissue； and a unit lockout rotatable about a pivot fixed to the handle. The unit lockout comprises an upper end near and under at least one blocking plate in the stapler； and another end facing the trigger to prevent it from firing when the upper end is blocked from upward movement by the at least one blocking plate. Whereas the upper end of the unit lockout is moved relative to the at least one blocking plate so that the upper end of unit lockout is no longer under the at least one blocking plate to permit the unit lockout to rotate about the pivot.
