In October 2023, the consumption tax will be shifted to the qualified invoice storage method (invoice system). While there are concerns about the impact of this change on the accounting department and accounting system, there may be many people who do not have an accurate understanding of the invoice system and "digital invoice". This document briefly summarizes the basic structure of consumption tax, overview of the invoice system, and frequently asked questions and answers, including how the practice should be after the transition to the invoice system, based on a lecture (delivered on May 26, 2021) by Hiroyuki Kato, Information and Communication Technology (IT) Strategy Office, Cabinet Secretariat, who is called "the key man of digital invoice. The presentation also includes a brief summary of the practical aspects after the transition to the invoice system.