An electrochemical capacitor capable of increasing a capacity is proposed. The electrochemical capacitor is a positive electrode and a negative electrode formed over a surface plane of a substrate. Additionally, the electrochemical capacitor has an electrolyte, and the positive electrode and the negative electrode are in contact with a same surface plane of the electrolyte. In other words, the electrochemical capacitor has a positive electrode active material and a negative electrode active material over a surface plane of an electrolyte, a positive electrode current collector which is in contact with the positive electrode active material, and a negative electrode current collector which is in contact with the negative electrode active material. By the aforesaid structure, a capacity of the electrochemical capacitor can be increased.