  We report the discovery of a triple-giant-planet system around an evolved
star HD 184010 (HR 7421, HIP 96016). This discovery is based on observations
from Okayama Planet Search Program, a precise radial velocity survey,
undertaken at Okayama Astrophysical Observatory between 2004 April and 2021
June. The star is K0 type and located at beginning of the red-giant branch. It
has a mass of $1.35_{-0.21}^{+0.19} M_{\odot}$, a radius of
$4.86_{-0.49}^{+0.55} R_{\odot}$, and a surface gravity $\log g$ of
$3.18_{-0.07}^{+0.08}$. The planetary system is composed of three giant planets
in a compact configuration: The planets have minimum masses of $M_{\rm{b}}\sin
i = 0.31_{-0.04}^{+0.03} M_{\rm{J}}$, $M_{\rm{c}}\sin i = 0.30_{-0.05}^{+0.04}
M_{\rm{J}}$, and $M_{\rm{d}}\sin i = 0.45_{-0.06}^{+0.04} M_{\rm{J}}$, and
orbital periods of $P_{\rm{b}}=286.6_{-0.7}^{+2.4}\ \rm{d}$,
$P_{\rm{c}}=484.3_{-3.5}^{+5.5}\ \rm{d}$, and $P_{\rm{d}}=836.4_{-8.4}^{+8.4}\
\rm{d}$, respectively, which are derived from a triple Keplerian orbital fit to
three sets of radial velocity data. The ratio of orbital periods are close to
$P_{\rm{d}}:P_{\rm{c}}:P_{\rm{b}} \sim 21:12:7$, which means the period ratios
between neighboring planets are both lower than $2:1$. The dynamical stability
analysis reveals that the planets should have near-circular orbits. The system
could remain stable over 1 Gyr, initialized from co-planar orbits, low
eccentricities ($e=0.05$), and planet masses equal to the minimum mass derived
from the best-fit circular orbit fitting. Besides, the planets are not likely
in mean motion resonance. HD 184010 system is unique: it is the first system
discovered to have a highly evolved star ($\log g < 3.5$ cgs) and more than two
giant planets all with intermediate orbital periods ($10^2\ \rm{d} < P < 10^3\
\rm{d}$).
