A continuous variable valve duration apparatus includes a camshaft, a cam unit on which a cam is formed and the camshaft is inserted, a guide bracket of which an upper guide boss is formed, an inner wheel transmitting the rotation of the camshaft to the cam unit, a wheel housing of which a guide shaft having a guide thread formed thereto to be movably inserted into the upper guide boss is formed thereto, and of which a tail guide guiding the relative movement of the guide bracket is formed thereto, and the wheel housing into which the inner wheel is rotatably inserted, a worm wheel of which an inner thread engaged with the guide thread is formed on inside thereof and of which an outer thread is formed on outside thereof, and a tolerance adjusting pin inserted into the tolerance adjusting portion.