Serial 2's Complementer with One Input and One Output
According to the State Table given by you,

S(t + 1) = X' + S(t)

Y = X + S(t).

But, in this circuit diagram Y turns out to be Y = X xor S(t).

Also according to your State Diagram Y turns out to be Y = X xor S(t).

So either the State Table is wrong and the State Diagram and the circuit is correct,

Or 

State Table is correct and the State Diagram and the circuit is wrong,