An aging device includes a semiconductor substrate, an element isolation insulating layer which is formed in a recessed portion of the semiconductor substrate and which has an upper surface higher than an upper surface of the semiconductor substrate, first and second element regions isolated by the element isolation insulating layer, first and second diffusion layers formed in the semiconductor substrate in the first element region, a first gate insulating film formed on the semiconductor substrate between the first and second diffusion layers, a second gate insulating film formed on the semiconductor substrate in the second element region, and a floating gate electrode formed on the first and second gate insulating films and formed to extend from the first element region to the second element region. The deepest portions of the first and second diffusion layers are isolated from the element isolation insulating layer.