  We discuss the accuracy of the estimation of the $n$ identical unknown
actions of $\SU(2)$ by using entanglement. This problem has a similar structure
with the phase estimation problem, which was discussed by Bu\v{z}ek, Derka, and
Massar\cite{BDM}. The estimation error asymptotically decreases to zero with an
order of $\frac{1}{n^2}$ at least.
