The present invention provides an aminoalcohol together with, as necessary, at least one selected from the group consisting of: at least one compound selected from the group consisting of urea and a urea derivative; a nonionic detergent; and sucrose to provide a biological material having an excellent light-transmitting property. The present invention provides a technique that allows a high-throughput observation of gene expression/localization or cell morphology in tissue at an whole-tissue level.