  We present the Atacama Large Millimeter/submillimeter Array (ALMA)
observation of the Sub-millimeter galaxy (SMG) ID 141 at z=4.24 in the [N II]
205 $\mu$m line (hereafter [N II]) and the underlying continuum at (rest-frame)
197.6 $\mu$m. Benefiting from lensing magnification by a galaxy pair at
z=0.595, ID 141 is one of the brightest z$>4$ SMGs. At the angular resolutions
of $\sim1.2"$ to $1.5"$ ($1" \sim6.9$ kpc), our observation clearly separates,
and moderately resolves the two lensed images in both continuum and line
emission at $\rm S/N>5$ . Our continuum-based lensing model implies an averaged
amplification factor of $\sim5.8$ and reveals that the de-lensed continuum
image has the S\'ersic index $\simeq 0.95$ and the S\'ersic radius of
$\sim0.18" (\sim 1.24$ kpc). Furthermore, the reconstructed [N II] velocity
field in the source plane is dominated by a rotation component with a maximum
velocity of $\sim 300$ km/s at large radii, indicating a dark matter halo mass
of $\sim 10^{12}M_{\odot}$. This, together with the reconstructed velocity
dispersion field being smooth and modest in value ($<100$ km/s) over much of
the outer parts of the galaxy, favours the interpretation of ID 141 being a
disk galaxy dynamically supported by rotation. The observed [N II]/CO (7-6) and
[N II]/[C II] 158 $\mu$m line luminosity ratios, which are consistent with the
corresponding line ratio vs. far-infrared color correlation from local luminous
infrared galaxies, imply a de-lensed star formation rate of ($1.8\pm
0.6)\times10^3M_\odot$/yr and provide an independent estimate on the size of
the star-forming region $0.7^{+0.3}_{-0.3}$ kpc in radius.

Astrophysics of Galaxies