  A developing supercritical collisionless shock propagating in a homogeneously
magnetized plasma of ambient gas origin having higher uniformity than the
previous experiments is formed by using high-power laser experiment. The
ambient plasma is not contaminated by the plasma produced in the early time
after the laser shot. While the observed developing shock does not have
stationary downstream structure, it possesses some characteristics of a
magnetized supercritical shock, which are supported by a one-dimensional full
particle-in-cell simulation taking the effect of finite time of laser-target
interaction into account.
