To reduce a running cost, to save resources, to reduce power consumption (to improve an energy saving property), to lower the cost of a washing device, and to make the entire device small-sized and light in weight, by reusing waste water.

When washing feeding bottles Gm... with washing liquid W, waste water We discharged from a discharge port part 12 which discharges, to the outside, heating water Wh and/or cooling water Wc in a milk sterilizer 10 having a sterilizing function Fs of heating a container 11 housing milk M by the heating water Wh and/or a cooling function Fc of cooling the sterilized container 11 housing the milk M by the cooling water Wc is used as the washing liquid W, and the feeding bottles Gm... are washed by jetting the washing liquid W to the feeding bottles Gm... as washing objects set to a prescribed position.