  The pressure ($p$) -- temperature ($T$) phase diagram for microscopic
magnetism in the multiferroic compound HoMn$_{2}$O$_{5}$ was established using
neutron diffraction measurements under a hydrostatic pressure up to 1.25 GPa.
At ambient pressure, incommensurate--commensurate--incommensurate magnetic
phase transitions occur successively with decreasing temperature. Upon applying
pressure, the incommensurate phase at the lowest temperature almost decreases
and the commensurate phase appears. The $p$ -- $T$ phase diagram established
shows excellent agreement with the recently reported $p$ -- $T$ dielectric
phase diagram, where ferroelectricity is induced by applying pressure. We also
found that the $p$ -- $T$ magnetic phase diagram is quite similar to the
previously obtained magnetic field-temperature phase diagram.
