PURPOSE: To soften cold seawater, increase pH, decompose and purify organic substances, protect a fish catch from putrefaction, discoloration and deterioration and prevent freshness from reducing by jetting magnetic air on the cold seawater in a fish hold.

CONSTITUTION: A magnetic air generator 2 is installed in a fish hold 1, equipped with freezing cooling pipes 4 and surrounded with a heat insulating wall 8 and magnetic air is jetted from jetters 3 connected through pipes (3a) onto the cold seawater 14 to provide uniform temperature and store a fish catch.