  This is a reply to W. Zawadzki's paper (arXiv: cond-mat/0701378) on
non-exietence of spin transverse force for a relativistic electron. The force
was first proposed by the present author that the spin current will experience
a transverse force in an electric field as a relativistic quantum mechanical
effect, and in semiconductor with Rahsba spin-orbit coupling. Zawadzki's
approach is based on an incorrect relation between the velocity and canonical
momentum, and his conclusion is not true.
