PURPOSE: To maintain stable anticorrosion and rustproofing effects for hours, by setting effective ingredients of an electric discharge machining fluid down to amine, polyacrylamide and/or a nonionic surface active agent.

CONSTITUTION: Polyacylamide and a nonionic surface active agent promoto amine's anticorrosion and rustproofing actions, whereby a remarkably excellent effect is securable owing to these synergetic interactions. At the time of machining for hours, the polyacylamide and the nonionic surface active agent are left behind in a machining fluid, whereas amine concentration is liable to be lowered in a time elapsing manner, so that this synergetic effect is maintained longer, therefore a stable anticorrosion effect is kept up for hours.