  We propose a method to estimate the pseudo jet opening half-angle of GRBs
using the spectral peak energy ($\Ep$)--peak luminosity relation (so called
Yonetoku relation) as well as the $\Ep$--collimation-corrected $\gamma$-ray
energy relation (so called Ghirlanda relation). For bursts with known jet break
times and redshifts, we compared the pseudo jet opening half-angle with the
standard one and found that the differences are within a factor 2. We apply the
method to 689 long GRBS. We found that the distribution function of the pseudo
jet opening half-angle obeys $f(\theta_j)\propto\theta_j^{-2.2 \pm 0.2}$ with
possible cutoffs for $\theta_j < 0.04$ and $\theta_j > 0.3$ although the
log-normal fit is also possible. $\theta^{-2}$ distribution is compatible with
the structured jet model. From the distribution function we found that the
beaming correction for the rate of GRBs is $\sim 340$, which means $\sim
10^{-5}$ yr$^{-1}$ galaxy$^{-1}$ or only one in $10^2$ type Ib/c supernovae. We
also found the evolution of the distribution function as a function of the
redshift.
