  Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid
sample return missions, not only because of its accessibility but also because
of the first C-type asteroid for exploration missions. The lightcurve-related
physical properties of this object were investigated during the 2011-2012
apparition. We aim to confirm the physical parameters useful for JAXA's
Hayabusa 2 mission, such as rotational period, absolute magnitude, and phase
function. Our data complement previous studies that did not cover low phase
angles. With optical imagers and 1-2 m class telescopes, we acquired the
photometric data at different phase angles. We independently derived the
rotational lightcurve and the phase curve of the asteroid. We have analyzed the
lightcurve of 162173 (1999 JU3), and derived a synodic rotational period of
7.625 +/- 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude H_R =
18.69 +/- 0.07 mag and the phase slope of G = -0.09 +/- 0.03 were also obtained
based on the observations made during the 2011-2012 apparition.
