To provide a method for producing the subject cleaning agent, capable of simply and inexpensively removing a slightly soluble liquid having high viscosity by sort-time treatment and remarkably improving filtering property by carrying out centrifugation before filtering a crude basic sulfurized alkaline earth metal phenate type cleaning agent.

A raw material mixture containing phenols, dihydric alcohols, an alkaline earth metal reagent comprising an alkaline earth metal oxide or hydroxide or a mixture thereof is reacted with sulfur in the presence or absence of water to carry out addition of metal and sulfuration and then, the reaction product is subjected to carbon dioxide treatment in the presence or absence of water and the product is centrifuged by centrifugal effect due to 3000 to 10000 G pressure and filtered and distilled. For example, a decanter type centrifugal separator can be used in order to carry out centrifugal separation. The centrifugal separation is carried out preferably at 160-180°C for 1-5min under 4,000 to 8,000 G pressure. The filtration is preferably carried out by using a filtering auxiliary having 1-50μm particle diameter, e.g. activated carbon and a filter having 100-300 mesh.