The present invention provides: a hot work tool steel which has excellent toughness and excellent quenching crack resistance; and a hot work tool. A hot work tool steel or hot work tool which is composed of, in mass%, 0.25-0.45% of C, 0.1-0.4% of Si, 0.5-0.9% of Mn, 0-0.6% of Ni, 4.9-5.5% of Cr, 1.3-2.3% of Mo or W by itself or 1.3-2.3% of (Mo + 1/2W) in combination, and 0.6-0.9% of V, with the balance being made up of Fe and impurities, and which is configured such that the value A is 6.00 or more and the value B is 1.00 or less, said values A and B being calculated by formula 1 and formula 2, respectively. In formulae 1 and 2, the atomic symbols in parentheses represent the contents (mass%) of the respective elements.Formula 1: Value A = -0.7(%Si) + 1.5(%Mn) + 1.3(%Ni) + 0.9(%Cr) + 0.6(%(Mo + 1/2W)) + 0.3(%V)Formula 2: Value B = 1.9(%C) + 0.043(%Si) + 0.12(%Mn) + 0.09(%Ni) + 0.042(%Cr) + 0.03(%(Mo + 1/2W)) - 0.12(%V)
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