  We report on the first open-use based Atacama Large Millimeter/submm Array
(ALMA) 345-GHz observation for the late afterglow phase of GRB131030A. The ALMA
observation constrained a deep limit at 17.1 d for the afterglow and host
galaxy. We also identified a faint submillimeter source (ALMAJ2300-0522) near
the GRB131030A position. The deep limit at 345 GHz and multifrequency
observations obtained using {\it Swift} and RATIR yielded forward shock
modeling with a two-dimensional relativistic hydrodynamic jet simulation and
described X-ray excess in the afterglow. The excess was inconsistent with the
synchrotron self-inverse Compton radiation from the forward shock. The host
galaxy of GRB131030A and optical counterpart of ALMAJ2300-0522 were also
identified in the SUBARU image. Based on the deep ALMA limit for the host
galaxy, the 3-$\sigma$ upper limits of IR luminosity and the star formation
rate (SFR) is estimated as $L_{IR}<1.11\times10^{11} L_{\odot}$ and SFR$<18.7$
($M_{\odot}$~yr$^{-1}$), respectively. Although the separation angle from the
burst location (3.5 arcsec) was rather large, ALMAJ2300-0522 may be one
component of the GRB131030A host galaxy, according to previous host galaxy
cases.
