Abstract: An electrolysis apparatus has a number of membrane electrolysis cells. Each of the cells has a membrane formed on both sides with a contact layer. The apparatus, while it is compact in its design, is also suitable for comparatively high hydrogen production rates and can consequently be used particularly flexibly. A contact plate is respectively arranged on each contact layer. Each of the contact plates is formed, on its surface facing the contact layer assigned to it, with a system of ducts for the transport of water and/or gas.