A surgical stapling instrument for performing a circular anastomosis stapling operation is provided. The surgical instrument includes a stapling head assembly mounted by a flexible support shaft to an actuator handle assembly. The support shaft is capable of bending in any radial direction relative to its centerline into a curved configuration suitable for insertion into a patient. The flexible support shaft includes a dual coil structure which is adapted to support itself in any curved configuration and to resist deflection upon insertion into the patient and actuation of the stapling head assembly. The stapling head assembly includes a driver assembly which is operable in multiple stages to separate the staple forming and tissue cutting actions to reduce the peak force required to operate the instrument. The actuator handle assembly includes a staple actuating lever and a cam follower assembly which operate in two stages with different mechanical advantages to facilitate the operation of the instrument by a surgeon. The actuator handle assembly includes a thumb wheel for opening and closing the anvil and an adjusting knob for adjusting the anvil gap. A control lever is provided for pivoting the stapling head assembly relative to the flexible support shaft.