The present invention relates to a maraging steel containing, in terms of mass %, 0.20≤C≤0.35, 9.0≤Co≤20.0, 1.0≤(Mo+W/2)≤2.0, 1.0≤Cr≤4.0, and a certain amount of Ni, with the balance being Fe and inevitable impurities, in which in a case where the contents of V and Nb satisfy V+Nb≤0.020 mass %, the amount of Ni is 6.0≤Ni≤9.4, and in which in a case where the contents of V and Nb satisfy 0.020 mass %