To provide a redox capacitor that can be used at room temperature and a manufacturing method thereof. Amorphous semiconductor including hydrogen is used as an electrolyte of a redox capacitor. As a typical example of the amorphous semiconductor including hydrogen, an amorphous semiconductor including a semiconductor element such as amorphous silicon, amorphous silicon germanium, or amorphous germanium can be used. As another example of the amorphous semiconductor including hydrogen, oxide semiconductor including hydrogen can be used. As typical examples of the oxide semiconductor including hydrogen, an amorphous semiconductor including a single-component oxide semiconductor such as zinc oxide, titanium oxide, nickel oxide, vanadium oxide, and indium oxide can be given. As another example of oxide semiconductor including hydrogen, a multi-component oxide semiconductor such as InMO3(ZnO)m (m>0 and M is one or more metal elements selected from Ga, Fe, Ni, Mn, and Co) can be used.