The present invention is an antimicrobially-treated material which has a coloring preventing function and is in contact with water or moisture or contains water, comprising (A) a silver-based antimicrobial agent which dissociates silver ions in the water system and (B) a silver ion trapping agent for trapping silver ions comprising one or more kinds of compounds selected from the group consisting of purine bases, pyrimidine bases, thiabendazole, and potassium iodide, wherein a ratio of (A)/(B) is 1/1 to 100/1 by weight.