It is an object of the present invention to provide a copper ion-producing composition that has a copper ion (mineral)-based germicidal activity against Legionella spp., Escherichia coli, Staphylococcus aureus, and saprophytic bacteria occurring in the water in drinking water storage tanks, hot springs, bathhouses, and pools, and that can supply mineral, and also to provide a granular composition that contains this copper ion-producing composition. The copper ion-producing composition is obtained by mixing 0.3 to 10 weight parts surfactant with 100 weight parts metallic copper powder. The granular composition is obtained by kneading this copper ion-producing composition with poorly water-soluble material that has a softening point of not less than 70.degree. C. The granular composition is also obtained by coating the copper ion-producing composition on the surface of poorly water-soluble material that has a softening point of not less than 70.degree. C.