The present invention provides a novel curable composition in which a reaction is caused to occur between a hydroperoxide and a thiourea compound to initiate polymerization of a radical polymerizable monomer and which has excellent adhesive properties, moderate curability, and excellent long-term storage stability. The present invention relates to a curable composition (A) containing: a radical polymerizable monomer (a1) having no acidic group； a hydroperoxide compound (a2)； and at least one cyclic thiourea compound (a3) selected from the group consisting of a substituted ethylenethiourea compound (a3-1), a substituted propylenethiourea compound (a3-2), and a substituted butylenethiourea compound (a3-3) each having a specific structure with a cyclic structure moiety into which a substituent is introduced.
