An interposer includes a wiring member including a first inorganic substrate, a reinforcement member including a second inorganic substrate, and an adhesive part interposed between the wiring member and the reinforcement member. Each of the first and second inorganic substrates includes first and second surfaces. Multiple inorganic insulating layers formed on the first surface of each of the first and second inorganic substrates have the same layer configuration and are arranged symmetrically in a vertical direction with the adhesive part centered therebetween. An inorganic insulating layer and an organic insulating layer formed on the second surface of each of the first and second inorganic substrates have the same layer configuration and are arranged symmetrically in the vertical direction with the adhesive part. An organic insulating layer formed on the second surface of each of the first and second inorganic substrates is an outermost insulating layer.