Providing a metal mold repair method and a metal mold repair paste agent which are capable of repairing cracks with simple work. A repair paste agent containing components that become an alloy is directly applied to a surface of a metal mold having a crack so as to cover the crack part, subsequently a surface of the repair paste agent is coated with an oxidation inhibitor and the repair paste agent is made to penetrate the inside of the crack by heating and becomes an alloy, thereby filling up the crack.