The present invention provides a sustained-release bactericidal and antimicrobial agent which does not necessitate complicated processes such as a bactericidally and antimicrobially treating apparatus or a device for continuously adding the agent, and continuously exhibits a bactericidally and antimicrobially treating property in an electrodeposition coating system. Specially, the present invention provides a sustained-release bactericidal and antimicrobial agent composed of a tablet or a briquette which contains l,2-ben2oisothiazolin-3-one or a sustained-release bactericidal and antimicrobial agent prepared by storing l,2-benzoisothiazolin-3-one in a water-permeable container. In addition, the present invention provides a method for bactericidally and antimicrobially treating a cation electrodeposition coating material, an electrolyte or a washing water which includes putting the sustained-release bactericidal and antimicrobial agent in an electrodeposition tank, an electrodeposition coating material storage tank, an electrolyte storage tank, a dip-washing tank, and a washing water storage tank and the like in a cation electrodeposition coating system and then dipping the agent in the cation electrodeposition coating material, the electrolyte or the washing water or placing the agent under the circulation of the cation electrodeposition coating material, the electrolyte or the washing water so as to gradually dissolve l,2-benzoisothiazolin-3-one in the cation electrodeposition coating material, the electrolyte or the washing water.
