We report the discovery and analysis of the planetary microlensing event OGLE-2017-BLG-0406, which was observed both from the ground and by the ${it Spitzer}$ satellite in a solar orbit. At high magnification, the anomaly in the light curve was densely observed by ground-based-survey and follow-up groups, and it was found to be explained by a planetary lens with a planet/host mass ratio of $q=7.0 times 10^{-4}$ from the light-curve modeling. The ground-only and ${it Spitzer}$-only data each provide very strong one-dimensional (1-D) constraints on the 2-D microlens parallax vector $bf{pi_{rm E}}$. When combined, these yield a precise measurement of $bf{pi_{rm E}}$, and so of the masses of the host $M_{rm host}=0.56pm0.07,M_odot$ and planet $M_{rm planet} = 0.41 pm 0.05,M_{rm Jup}$. The system lies at a distance $D_{rm L}=5.2 pm 0.5 {rm kpc}$ from the Sun toward the Galactic bulge, and the host is more likely to be a disk population star according to the kinematics of the lens. The projected separation of the planet from the host is $a_{perp} = 3.5 pm 0.3 {rm au}$, i.e., just over twice the snow line. The Galactic-disk kinematics are established in part from a precise measurement of the source proper motion based on OGLE-IV data. By contrast, the ${it Gaia}$ proper-motion measurement of the source suffers from a catastrophic $10,sigma$ error.
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