A method of producing a nickel-cobalt composite hydroxide includes: preparing a first solution containing nickel ions and cobalt ions; preparing a second solution containing tungsten ions and having a pH of 10 or more; preparing a third solution containing a complex ion-forming factor; preparing a liquid medium having a pH in a range of 10 to 13.5; supplying the first solution, the second solution, and the third solution separately and simultaneously to the liquid medium to obtain a reacted solution having a pH in a range of 10 to 13.5; and obtaining the nickel-cobalt composite hydroxide containing nickel, cobalt, and tungsten from the reacted solution.