A high tensile strength steel having a chemical composition comprising, by mass%, C: 0.01 to 0.10%, Si: 0.01 to 0.50%, Mn: 0.80 to 2.50%, P: 0.020% or less, S: 0.001 to 0.010%, Cu: 0.80 to 1.50%, Ni: 0.20 to 1.50%, Al: 0.003% or less, Ti: 0.005 to 0.030%, N: 0.003 to 0.008%, O: 0.0005 to 0.0050%, Nb: 0 to 0.030%, Mo: 0 to 0.80%, Cr: 0 to 0.80%, B: 0 to 0.0020%, V: 0 to 0.050%, Ca: 0 to 0.005%, Mg: 0 to 0.01%, REM: 0 to 0.01%, and the balance: Fe and impurities, wherein: a cracking parameter of material Pcm shown by formula below is 0.25 or less; Cu particles having a major axis of 1 nm or more are dispersed in the steel, and an average value of an equivalent circular diameter of the Cu particles is in a range of 4 to 25 nm, and a plane-converted distribution amount of the Cu particles is in a range of 3 to 20%, wherein the major axis, average value of an equivalent circular diameter, and plane-converted distribution amount are determined as disclosed in the description; a composite inclusion in which MnS is present around a Ti oxide is contained in the steel; an area fraction of the MnS in a cross-section of the composite inclusion is 10% or more and less than 90%; a proportion that the MnS accounts for in a peripheral length of the composite inclusion is 10% or more; and a number density of the composite inclusions which have a grain diameter in a range of 0.5 to 5.0 μm is in a range of 10 to 100 per mm 2, wherein the area fraction of the MnS, proportion that the MnS accounts for in a peripheral length, number density of the composite inclusions, and grain diameter are determined as disclosed in the description; Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5 B where, each symbol of an element in formula represents a content (mass%) of the relevant element. C: 0.01 to 0.10%, Si: 0.01 to 0.50%, Mn: 0.80 to 2.50%, P: 0.020% or less, S: 0.001 to 0.010%, Cu: 0.80 to 1.50%, Ni: 0.20 to 1.50%, Al: 0.003% or less, Ti: 0.005 to 0.030%, N: 0.003 to 0.008%, O: 0.0005 to 0.0050%, Nb: 0 to 0.030%, Mo: 0 to 0.80%, Cr: 0 to 0.80%, B: 0 to 0.0020%, V: 0 to 0.050%, Ca: 0 to 0.005%, Mg: 0 to 0.01%, REM: 0 to 0.01%, and the balance: Fe and impurities, wherein: a cracking parameter of material Pcm shown by formula below is 0.25 or less; Cu particles having a major axis of 1 nm or more are dispersed in the steel, and an average value of an equivalent circular diameter of the Cu particles is in a range of 4 to 25 nm, and a plane-converted distribution amount of the Cu particles is in a range of 3 to 20%, wherein the major axis, average value of an equivalent circular diameter, and plane-converted distribution amount are determined as disclosed in the description; a composite inclusion in which MnS is present around a Ti oxide is contained in the steel; an area fraction of the MnS in a cross-section of the composite inclusion is 10% or more and less than 90%; a proportion that the MnS accounts for in a peripheral length of the composite inclusion is 10% or more; and a number density of the composite inclusions which have a grain diameter in a range of 0.5 to 5.0 μm is in a range of 10 to 100 per mm 2, wherein the area fraction of the MnS, proportion that the MnS accounts for in a peripheral length, number density of the composite inclusions, and grain diameter are determined as disclosed in the description; Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5 B where, each symbol of an element in formula represents a content (mass%) of the relevant element. a cracking parameter of material Pcm shown by formula below is 0.25 or less; Cu particles having a major axis of 1 nm or more are dispersed in the steel, and an average value of an equivalent circular diameter of the Cu particles is in a range of 4 to 25 nm, and a plane-converted distribution amount of the Cu particles is in a range of 3 to 20%, wherein the major axis, average value of an equivalent circular diameter, and plane-converted distribution amount are determined as disclosed in the description; a composite inclusion in which MnS is present around a Ti oxide is contained in the steel; an area fraction of the MnS in a cross-section of the composite inclusion is 10% or more and less than 90%; a proportion that the MnS accounts for in a peripheral length of the composite inclusion is 10% or more; and a number density of the composite inclusions which have a grain diameter in a range of 0.5 to 5.0 μm is in a range of 10 to 100 per mm 2, wherein the area fraction of the MnS, proportion that the MnS accounts for in a peripheral length, number density of the composite inclusions, and grain diameter are determined as disclosed in the description; Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5 B where, each symbol of an element in formula represents a content (mass%) of the relevant element.