The threshold electric field E(T) for the depinning of the SDW was inv
estigated in (TMTSF)2ClO4 with varying the degree of anion ordering. I
n the rapidly quenched phase, the observed temperature dependence of E
(T) was explained by the weak impurity pinning. On the other hand, the
strong pinning was found to be effective in the slowly quenched phase
. This change of pinning mechanism was attributed to the change of ani
on disorder as an impurity potential.