  We solve spherically symmetric radiation flows under full special relativity
with the help of a variable Eddington factor $f(\tau, \beta)$, where $\tau$ is
the optical depth and $\beta$ is the flow velocity normalized by the speed of
light. Relativistic radiation hydrodynamics under the moment formalism has
several complex problems, such as a closure relation. Conventional moment
equations closed with the traditional Eddington approximation in the comoving
frame have singularity, beyond which the flow cannot be accelerated. In order
to avoid such a pathological behavior inherent in the relativistic moment
formalism, we propose a variable Eddington factor, which depends on the flow
velocity as well as the optical depth, for the case of the sperically symmertic
one-dimensional flow. We then calculate the relaticistic spherical flow with
such variable Eddington factors to investigate the case that gas is accelerated
by radiative force. As a result, it is shown that the gas speed reaches around
the speed of light by radiation pressure.
