Code Review is an essential activity to ensure the quality of the software in the development process. Code Review Automation with various analyses can reduce human efforts of code review activities. However, it is a challenge to automate the code review process for large-scale companies such as Samsung Electronics due to their complex development environments: many kinds of products, various sizes of software, different version control systems, and diverse code review systems. In this work, we show how we automated the code review process for those intricate environments, and share some lessons learned during two years of operation. Our unified code review automation system, Code Review Bot, is designed to process review requests holistically regardless of such environments, and checks various quality-assurance items such as potential defects in the code, coding style violations, test coverage, architectural smells, and open source license violations. Some key findings include: 1) about 60% of issues found by Code Review Bot were reviewed and fixed in advance of product releases, 2) more than 70% of developers gave positive feedback about the system, 3) developers rapidly and actively responded to reviews, and 4) the automation did not much affect the amount or the frequency of human code reviews compared to the internal policy to encourage developers to participate in code review activities. Our findings provide practical evidence that automating code review helps assure software quality.