  Magnetic dipole moment and mean-square charge radius of $^{199}$Pt
($I^{\pi}=$ 5/2$^-$) have been evaluated for the first time from the
investigation of the hyperfine splitting of the $\lambda_1=$ 248.792 nm
transition by in-gas-cell laser ionization spectroscopy. Neutron-rich nucleus
$^{199}$Pt was produced by multi-nucleon transfer reaction at the KISS where
the nuclear spectroscopy in the vicinity of $N=$ 126 is planed from the aspect
of an astrophysical interest as well as the nuclear structure. Measured
magnetic dipole moment $+$0.63(13)$\mu_{\rm N}$ is consistent with the
systematics of those of nuclei with $I^{\pi}=$ 5/2$^-$. The deformation
parameter $|<\beta_2^2>^{1/2}|$ evaluated from the isotope shift indicates the
gradual shape change to spherical shape of platinum isotopes with increasing
neutron number toward $N=$ 126.
