  We have investigated dielectric properties in a series of crystals of
$R$MnO$_{3}$ ($R$ is a rare earth ion) under magnetic fields and
quasihydrostatic pressure. We have found that ferroelectric phase appeared in
GdMnO$_3$ crystal below 13K. We have confirmed that a small spontaneous
polarization exists along a axis ($P_a$) in the orthorhombic $Pbnm$ setting and
that $P_a$ can be reversed by the dc electric field. The dielectric anomaly due
to the ferroelectric transition accompanied thermal hysteresis and lattice
striction. The ferroelectric transition temperature decreased with
quasihydrostatic pressure. These results indicate that the ferroelectric
transition is improper and is of the first-order displacement-type one. $P_a$
was easily collapsed by application of magnetic field of 0.4T parallel to the
spin-canting direction ($H \| c$) while it was enhanced parallel to the easy
axis ($H \| b$).
