  KCuCl$_3$ is a three dimensionally coupled spin dimer system, which undergoes
a pressure-induced quantum phase transition from a gapped ground state to an
antiferromagnetic state at a critical pressure of $P_{\rm c} \simeq 8.2$ kbar.
Magnetic excitations in KCuCl$_3$ at a hydrostatic pressure of 4.7 kbar have
been investigated by conducting neutron inelastic scattering experiments using
a newly designed cylindrical high-pressure clamp cell. A well-defined single
excitation mode is observed. The softening of the excitation mode due to the
applied pressure is clearly observed. From the analysis of the dispersion
relations, it is found that an intradimer interaction decreases under
hydrostatic pressure, while most interdimer interactions increase.
