This paper inquires into the essence of the bank note and the seigniorage in central bank, and in the light of this inquiry this paper presents a unified accounting understanding of the bank note issued by central bank and of the coin issued by government. It is indispensable to the financial soundness of central bank that central bank grasps the essence of the bank note and the coin and that it does accurately accounting for them. Furthermore, the financial soundness is essential in maintaining the credibility of central bank and it forms the basis of accomplishing the mission of central bank. This paper consists of as follows: (1) the views over the nature of the modern bank note (inconvertible bank note) are investigated and the reason why bank note is debt is explained. (2) the essence of the seigniorage and its accounting understanding are discussed, and the accounting methods of the seigniorage in current central bank are assessed. (3) the details of the accounting of the bank note and the coin are investigated concretely. (4) being based on the nature of debt in currency, a unified accounting understanding of the bank note and the coin is presented conceptually.