  We develop a time-dependent multi-group multidimensional relativistic
radiative transfer code, which is required to numerically investigate radiation
from relativistic fluids involved in, e.g., gamma-ray bursts and active
galactic nuclei. The code is based on the spherical harmonic discrete ordinate
method (SHDOM) that evaluates a source function including anisotropic
scattering in spherical harmonics and implicitly solves the static radiative
transfer equation with a ray tracing in discrete ordinates. We implement
treatments of time dependence, multi-frequency bins, Lorentz transformation,
and elastic Thomson and inelastic Compton scattering to the publicly available
SHDOM code. Our code adopts a mixed frame approach; the source function is
evaluated in the comoving frame whereas the radiative transfer equation is
solved in the laboratory frame. This implementation is validated with various
test problems and comparisons with results of a relativistic Monte Carlo code.
These validations confirm that the code correctly calculates intensity and its
evolution in the computational domain. The code enables us to obtain an
Eddington tensor that relates first and third moments of intensity (energy
density and radiation pressure) and is frequently used as a closure relation in
radiation hydrodynamics calculations.
