  Hadron masses under strong magnetic fields are studied. In the presence of
strong magnetic fields exceeding the QCD energy scale $ eB \gg \Lambda^2_{\rm
QCD} $, ${\rm SU(3)}_{\rm flavor} \otimes {\rm SU(2)}_{\rm spin}$ symmetry of
hadrons is explicitly broken so that the quark components of hadrons differ
from those with zero or weak magnetic fields $ eB \lesssim \Lambda^2_{\rm QCD}
$. Also, squeezing of hadrons by strong magnetic fields affects the hadron mass
spectrum. We develop a quark model which appropriately incorporates these
features and analytically calculate various hadron masses including mesons,
baryons and those with strangeness.
