It is often overlooked that so far, there has been inconsistency between the definition of the ampere in SI units and its realization. For instance, the ampere is defined based on the classical Ampere’s law, while its representation has been made through the Ohm’s law, that is, the ratio of the Josephson voltage to the quantum Hall resistance that do not belong to the SI units. However, in the revised SI units that are slated to take effect in 2019 on World Metrology Day, 20 th of May, it is significant to note that the ampere will be defined as a flow of electrons with the numerical value of the elementary charge fixed. In this instance, all three of the electrical units, such as the current, voltage and resistance will become defined on the basis of quantum physics. As a candidate for the quantum current standard, the various types of single electron pump devices are reviewed in relation to the redefinition of the ampere.