The hydrometallurgical Process for a nickel oxide ore, which is capable of preventing inevitable operation shutdown of a leaching step and maintaining high operation efficiency as a whole process, in a trouble of the steps other than the leaching step, in a hydrometallurgical Process for a nickel oxide ore using a High Pressure Acid Leach.It is characterized in that, the hydrometallurgical Process for a nickel oxide ore using a High Pressure Acid Leach equipment equipped with the following means (a) to (c), in a trouble of the steps other than the above leaching step, the leached slurry discharged from the means (c), which is used in the above High Pressure Acid Leach equipment, is subjected to self-circulation inside the High Pressure Acid Leach equipment, by transferring to the means (a), which is used in the above High Pressure Acid Leach equipment, as well as by shutdown of receiving the ore slurry and the addition of sulfuric acid, in the above leaching step: means (a) to preliminarily increase temperature and pressure of the ore slurry; means (b) to form the leached slurry, by the addition of sulfuric acid to the ore slurry with preliminarily increased temperature and pressure, and leaching under blow of high-pressure steam and high-pressure air; means (c) to eliminate a pressurized state of the leached slurry formed.