A curable sensitizer that exhibits a radical-polymerization sensitizing ability that conventional sensitizers do not have in a polymerization reaction using radicals, and is easily available at a low cost, a photocurable material containing the sensitizer, a cured product of the photocurable material, and a material for a wiring harness containing the photocurable material. The curable sensitizer contains an alcohol (meth)acrylate synthesized from an alcohol having one or more hydroxy groups and two or more oxygen atoms in a molecule and a (meth) acrylate ingredient selected from a (meth)acrylic acid and a derivative thereof. An ester bond is formed between one of the hydroxy groups of the alcohol and the (meth)acrylate ingredient. The sensitizer is capable of increasing curability of a curable material when mixed in the material. The photocurable material contains the curable sensitizer and a photoinitiator. The material for the wiring harness contains the photocurable material.