A method for producing a non-magnetic high-hardness alloy, comprising: - preparing a material having a Ni-based alloy composition containing, by weight%: C of 0.1% or less; Si of 2.0% or less; Mn of 2.0% or less; P of 0.03% or less; S of 0.01% or less; Cr of 30% to 45%; Al of 1.5% to 5%; the alloy composition optionally containing Ti of 3.0% or less, Zr of 3.0% or less, and Hf of 3.0% or less, satisfying the relationship Ti+Zr+Hf of 3.0% or less; Nb of 3.0% or less, Ta of 3.0% or less, and V of 3.0% or less, satisfying the relationship Nb+Ta+V of 3.0% or less; Co of 10% or less; Mo of 10% or less, and W of 10% or less, satisfying the relationship Mo+0.5W of 10% or less; Cu of 5% or less; B of 0.015% or less; Mg of 0.01% or less; Ca of 0.01% or less; REM (rare earth metal) of 0.1% or less; and Fe of 5% or less; and the balance Ni and unavoidable impurities; wherein the preparing comprises vacuum melting the raw material, and then homogenizing the material; - making an intermediate product, wherein making the intermediate product comprises hot forging, and subjecting same to a solution treatment (Heat Treatment 1), and wherein the solution treated intermediate product is subjected to peeling; - subjecting the heat-treated intermediate product to plastic working at a temperature of 700°C or less with a working rate of 15% or higher; and then - subjecting the plastically worked product to direct ageing treatment at a temperature of 350°C to 700°C. - preparing a material having a Ni-based alloy composition containing, by weight%: C of 0.1% or less; Si of 2.0% or less; Mn of 2.0% or less; P of 0.03% or less; S of 0.01% or less; Cr of 30% to 45%; Al of 1.5% to 5%; the alloy composition optionally containing Ti of 3.0% or less, Zr of 3.0% or less, and Hf of 3.0% or less, satisfying the relationship Ti+Zr+Hf of 3.0% or less; Nb of 3.0% or less, Ta of 3.0% or less, and V of 3.0% or less, satisfying the relationship Nb+Ta+V of 3.0% or less; Co of 10% or less; Mo of 10% or less, and W of 10% or less, satisfying the relationship Mo+0.5W of 10% or less; Cu of 5% or less; B of 0.015% or less; Mg of 0.01% or less; Ca of 0.01% or less; REM (rare earth metal) of 0.1% or less; and Fe of 5% or less; and the balance Ni and unavoidable impurities; wherein the preparing comprises vacuum melting the raw material, and then homogenizing the material; C of 0.1% or less; Si of 2.0% or less; Mn of 2.0% or less; P of 0.03% or less; S of 0.01% or less; Cr of 30% to 45%; Al of 1.5% to 5%; Ti of 3.0% or less, Zr of 3.0% or less, and Hf of 3.0% or less, satisfying the relationship Ti+Zr+Hf of 3.0% or less; Nb of 3.0% or less, Ta of 3.0% or less, and V of 3.0% or less, satisfying the relationship Nb+Ta+V of 3.0% or less; Co of 10% or less; Mo of 10% or less, and W of 10% or less, satisfying the relationship Mo+0.5W of 10% or less; Cu of 5% or less; B of 0.015% or less; Mg of 0.01% or less; Ca of 0.01% or less; REM (rare earth metal) of 0.1% or less; and Fe of 5% or less; and the balance Ni and unavoidable impurities; - making an intermediate product, wherein making the intermediate product comprises hot forging, and subjecting same to a solution treatment (Heat Treatment 1), and wherein the solution treated intermediate product is subjected to peeling; - subjecting the heat-treated intermediate product to plastic working at a temperature of 700°C or less with a working rate of 15% or higher; and then - subjecting the plastically worked product to direct ageing treatment at a temperature of 350°C to 700°C.