  We compute the kinematical dependence of the peak luminosity, the pulse width
and the spectral lag of the peak luminosity on the viewing angle $\theta_v$ of
a jet. For appropriate model parameters we obtain the peak luminosity-spectral
lag relation similar to the observed one including GRB980425. A bright (dim)
peak with short (long) spectral lag corresponds to a jet with small (large)
viewing angle. This suggests that the viewing angle of the jet might cause
various relations in GRBs such as the peak luminosity-variability relation and
the luminosity-width relation. Our model also suggests that X-ray rich GRBs (or
X-ray flushes or Fast X-ray transients) are typical GRBs observed from large
$\theta_v$ with large spectral lag and low variability.
