A hollow part is formed in a silicon substrate through the front and the back. A vibration electrode plate is arranged on an upper surface of the silicon substrate to cover the opening on the upper surface. A fixed electrode plate covers the upper side of the vibration electrode plate while maintaining a microscopic gap with the vibration electrode plate, where the peripheral part is fixed to the upper surface of the silicon substrate. The fixed electrode plate has the portion facing the upper surface of the silicon substrate through a space supported by a side wall portion arranged on an inner edge of the portion fixed to the upper surface of the silicon substrate without interposing a space. The outer surface of the side wall portion of the fixed electrode plate is covered by a reinforcement film made of metal such as Au, Cr, and Pt.