The present traverse hardening device performs traverse hardening on a shaft-like body which includes a main body part, and a large-diameter part provided in a part of the main body part in an axial direction and having an outer diameter larger than that of the main body part, the shaft-like body being disposed such that an axis thereof is directed along a vertical direction. The traverse hardening device includes: a heating unit which heats the shaft-like body; a cooling unit including a through hole which penetrates in the vertical direction and through which the shaft-like body is inserted, and an injection hole formed on an inner circumferential surface of the through hole and configured to inject a cooling liquid; and a guide cylinder in which an inner diameter of a lower end is smaller than an inner diameter of an upper end and at least a part thereof is disposed below the cooling unit and through which the shaft-like body is inserted.
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