The present invention provides a hydrometallurgical method for nickel oxide ore, wherein the plant can be smoothly started up without imposing a load onto a filter cloth for a separation treatment of zinc sulfide, and the amount of residual zinc in a mother liquor for nickel recovery can be reduced to 1 mg/L. In the plant start-up after the completion of a periodic inspection, a post-neutralization solution is controlled to return to a neutralization reaction tank via circulation piping by adjustment of a switching valve in flow piping without sulfurizing post-neutralization solution. When the flow rate and/or the temperature of the post-neutralization solution circulated reaches a predetermined value, a sulfurization treatment is applied to the post-neutralization solution in the dezincification reaction tank to form zinc-sulfide-containing mother liquor for nickel recovery and adjust the switching valve. Zinc-sulfide-containing mother liquor for nickel recovery is transferred to a filter apparatus via transfer piping.