To provide alloy tool steel having a quenching temperature lower than that of conventional matrix high speed steel and also having the same characteristics such as hardness and toughness after heat treatment, as those of conventional alloy tool steel, and to provide its manufacturing method and a die using it. The alloy tool steel has a composition which contains prescribed amounts of C, Si, Mn, P, S, Cu, Ni, Cr, Mo or/and W, V, Al, O and N and further contains prescribed amounts of one or more elements among Co, Nb, Ti, B, Ta, Zr, Pb, Bi, Ca, Te, Se, REM and Mg and has the balance Fe with inevitable impurities and in which inequality -0.2<[Delta]C<0.2 (where [Delta]C=C-(0.06*Cr+0.063*Mo+0.033*W+0.2*V+0.1*Nb)) is satisfied and the value of Lc defined by equation Lc=(8.8*Mo+5.9*W+50*V+40*Nb)/(6*Cr) is made to 1.0 to 2. (C)2004,JPO.