A repair method of a cast steel member having a crack formed on a surface of the cast steel member includes: forming a recess having a wedge-shaped cross section that widens in a depth direction of the cast steel member by cutting the cast steel member from the surface of the cast steel member to a predetermined depth so as to include the crack; pushing and embedding a repair member made of a metal material more flexible than the cast steel member into the recess formed in the recess forming; and diffusion-bonding the repair member to the cast steel member by heating a boundary between an exposed surface.
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