  The propagators of unstable particles are considered in the framework of the
convolution representation. Spectral function was found for a special case when
the propagator of scalar unstable particle has Breight-Wigner form. The
expressions for the dressed propagators of unstable vector and spinor fields
are derived in an analytical way for this case. We got the propagators in
modified Breit-Wigner forms which correspond to the complex-mass definition.
