  We report the first detection of linearly polarized emission at an observing
wavelength of 350 $\mu$m from the radio-loud Active Galactic Nucleus 3C 279. We
conducted polarization observations for 3C 279 using the SHARP polarimeter in
the Caltech Submillimeter Observatory on 2014 March 13 and 14. For the first
time, we detected the linear polarization with the degree of polarization of
13.3\%$\pm$3.4\% ($3.9\sigma$) and the Electric Vector Position Angle (EVPA) of
34.7$^\circ\pm5.6^\circ$. We also observed 3C~279 simultaneously at 13, 7, and
3.5 mm in dual polarization with the Korean very long baseline interferometry
(VLBI) Network on 2014 March 6 (single dish) and imaged in milliarcsecond (mas)
scales at 13, 7, 3.5, and 2.3 mm on March 22 (VLBI). We found that the degree
of linear polarization increases from 10\% to 13\% at 13 mm to 350 $\mu$m and
the EVPAs at all observing frequencies are parallel within $<10^\circ$ to the
direction of the jet at mas scale, implying that the integrated magnetic fields
are perpendicular to the jet in the innermost regions. We also found that the
Faraday rotation measures RM are in a range of $-6.5\times10^2 \sim
-2.7\times10^3$ rad m$^{-2}$ between 13 and 3.5 mm, and are scaled as a
function of wavelength: $|{\rm RM}|\propto\lambda^{-2.2}$. These results
indicate that the mm and sub-mm polarization emission are generated in the
compact jet within 1~mas scale and affected by a Faraday screen in or in the
close proximity of the jet.
