  We discuss stationary and axisymmetric trans-magnetosonic outflows in the
magnetosphere of a rotating black hole (BH). Ejected plasma from the plasma
source located near the BH is accelerated far away to form a relativistic jet.
In this study, the plasma acceleration efficiency and conversion of fluid
energy from electromagnetic energy are considered by employing the trans-fast
magnetosonic flow solution derived by Takahashi & Tomimatsu (2008). Considering
the parameter dependence of magnetohydrodynamical flows, we search for the
parameters of the trans-magnetosonic outflow solution to the recent M87 jet
observations and obtain the angular velocity values of the magnetic field line
and angular momentum of the outflow in the magnetized jet flow. Therefore, we
estimate the locations of the outer light surface, Alfv\'en surface, and
separation surface of the flow. We also discuss the electromagnetic energy flux
from the rotating BH (i.e., the Blandford-Znajek process), which suggests that
the energy extraction mechanism is effective for the M87 relativistic jet.
