  We have studied the pressure effect on magnetostriction, both in the
$ab$-plane and along the c-axis, of a (La,Pr)$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$
bilayered manganite single crystal over the temperature region where the
field-induced ferromagnetic metal (FMM) transition takes place. For comparison,
we have also examined the pressure dependence of magnetization curves at the
corresponding temperatures. The applied pressure reduces the critical field of
the FMM transition and it enhances the remanent magnetostriction. An anomalous
pressure effect on the remanent lattice relaxation is observed and is similar
to the pressure effect on the remanent magnetization along the c-axis. These
findings are understood from the view point that the double-exchange
interaction driven FMM state is strengthened by application of pressure.
