  We carried out zero-field muon-spin-rotation (ZF-$\mu$SR) measurements in
hydrostatic pressures in impurity-doped quantum spin gap system
Tl(Cu$_{0.985}$Mg$_{0.015}$)Cl$_3$ to investigate microscopic magnetic
properties of the pressure-induced phase. The spontaneous muon spin precession,
which indicates the existence of a long-range coherent order, is observed in
pressures. With decreasing temperature in 3.1 kbar, the internal static
magnetic field at the muon sites {\it H}$_{\rm int}$ tends to saturate to 280
Oe around 4 K, however, decreases to 240 Oe at 2.3 K. These results suggest a
rearrangement of ordered spins, and we speculate that the oblique
antiferromagnetic phase, which is observed in the pressure of 14 kbar on the
pure TlCuCl$_3$, appears in the Mg-doped system in lower pressures.
