This invention provides a method of producing a glass base material laminate, a method of producing an optical element, an optical element, and a concentrating photovoltaic device that can reliably bond a bonding surface between a glass base material and a transparent acrylic resin over a long period with high adhesiveness even under a high-temperature and high-humidity environment. In the method of producing an optical element, the optical element includes a glass substrate (5) and a sheet-like formed body (6) formed of an organic resin one surface of which has a fresnel lens pattern (6a) and the other surface of which is bonded to the glass substrate (5). The sheet-like formed body (6) is a thermoplastic polymer composition. A bonding surface (6b) of the sheet-like formed body (6) facing the glass substrate (5) is performed with surface treatment by irradiating active energy. A bonding surface (5a) of the glass substrate (5) facing the sheet-like formed body (6) is bonded to the bonding surface (6b) of the sheet-like formed body (6) by using a silane coupling agent as a crosslinking agent.