  We examine if the cosmological relaxation mechanism, which was proposed
recently as a new solution to the hierarchy problem, can be compatible with
high reheating temperature well above the weak scale. As the barrier potential
disappears at high temperature, the relaxion rolls down further after the
reheating, which may ruin the successful implementation of the relaxation
mechanism. It is noted that if the relaxion is coupled to a dark gauge boson,
the new frictional force arising from dark gauge boson production can
efficiently slow down the relaxion motion, which allows the relaxion to be
stabilized after the electroweak phase transition for a wide range of model
parameters, while satisfying the known observational constraints.
