An exhaust mechanism of a pneumatic nailing in which a striking cylinder is accommodated in a body and a striking piston in the striking cylinder is driven to drive a nail when compressed air is supplied to and exhausted from an upper portion of the striking cylinder, comprises: an inner cap arranged in the upper portion of the striking cylinder; a cylinder cap covering the inner cap; an exhaust chamber formed along inside the body between the inner cap and the cylinder cap; and a throttle hole formed in a lower portion of the exhaust chamber, wherein the exhaust air exhausted from the upper portion of the striking cylinder is discharged from the throttle hole via the exhaust chamber.