  The roton excitation in the superfluid He-4 does not possess a stationary
dipole moment. However, a roton has an instantaneous dipole moment, such that
at any given moment one can find it in the state either with positive or with
negative dipole moment projection on its momentum direction. The instantaneous
value of electric dipole moment of roton excitation is evaluated. The result is
in reasonable agreement with recent experimental observation of the splitting
of microwave resonance absorption line at roton frequency under external
electric field.
