  We study the phenomenon of macroscopic quantum tunneling (MQT) in a finite
size Josephson junction (JJ) with an externally applied magnetic field. As it
is well known, the problem of MQT in a point-like JJ is reduced to the study of
the under-barrier motion of a quantum particle in the washboard potential. In
the case of a finite size JJ placed in magnetic field, this problem is
considerably more complex since, besides the phase, the potential itself,
depends on space variables. We find the general expressions both for the
crossover temperature $T_{0}$ between thermally activated and macroscopic
quantum tunneling regimes and the escape time $\tau_{\mathrm{esc}}$. It turns
out that in proximity of particular values of magnetic field the crossover
temperature can vary non-monotonically.
