The present invention provides a method for washing a hard article, the method including: the contact step of bringing a detergent liquid obtained by mixing (a) a potassium internal olefin sulfonate and (b) water having a hardness of 5° DH or more, into contact with the hard article, and the step of rinsing the hard article after the contact step with water having a hardness of 5° DH or more, wherein the detergent liquid at 30° C. or more is brought into contact with the hard article in at least a part of the contact step.