The problem addressed by the present invention is to provide an apparatus for preparing ultrathin graphene pieces capable of preparing ultrathin graphene pieces in which less than 10 pieces of graphene are overlapped in large quantities, a method for preparing ultrathin graphene pieces capable of preparing the ultrathin graphene pieces with high yield, an ultrathin graphene piece in which less than 10 pieces of graphene are overlapped, a capacitor having high performance by using the ultrathin graphene piece as an electrode, and an efficient method of manufacturing the capacitor. The above-described problem can be solved by using an apparatus 20 for preparing ultrathin graphene pieces, the apparatus comprising: a graphite electrode 21; a counter electrode 22 which is made of graphite, a corrosion resistant alloy, or a precious metal; an electrolytic solution 25 in which one end sides of the two electrodes 21 and 22 are immersed; a container 24 which stores the electrolytic solution 25; and a power source 28 which is connected to the two electrodes 21 and 22 via wirings 26 and 27. The apparatus is also provided with a porous filter 23 so as to cover at least the immersed part of the graphite electrode 21 that is immersed in the electrolytic solution 25.