A microcapsule includes a core/shell structure, in which the shell includes a water-soluble polymer and the core includes an organic peroxide. The water-soluble polymer is preferably at least one water-soluble polymer selected from the group consisting of polyvinyl alcohol, gelatin, poly(meth)acrylic acid derivatives, polyvinyl pyrrolidone, and polyethylene oxide. The polyvinyl alcohol is preferably partially saponified polyvinyl alcohol having a degree of saponification of 80% by mole or more and 99.5% by mole or less and an average degree of polymerization of 1,500 or more and 3,500 or less.