  We investigate evolution of star clusters in external tidal field by means of
$N$-body simulations. We followed seven sets of cluster models whose central
concentration and strength of the tidal field are different. We found that the
mass loss timescale due to escape of stars, $t_{mloss}$, and its dependence on
the two-body relaxation timescale, $t_{rh,i}$, are determined by the strength
of the tidal field. The logarithmic slope [$= dln(t_{mloss})/dln(t_{rh,i})$]
approaches to near unity for the cluster models in weaker tidal field. The
timescale and the dependence are almost independent of the central
concentration for clusters in the tidal field of the same strength. In our
results, the scaling found by Baumgardt (2001) can be seen only in the cluster
models with moderately strong tidal field.
