Business rules can be implemented on business processes, business behavior, people, or software in an organization. Aligned with software development, business rules are captured from requirement elicitation and analysis, then designed and implemented in the software. The changes of business environment may affect business rules. The changes of the business rules may bring impact in the software, so that the software needs to be redeveloped. In this paper, we present a source code generator to automate business rule implementation using business rule approach. We propose a Domain Specific Language (DSL) of business rule to help expressing business rules in a business-friendly language. We also develop a business rule generator to generate source codes based on a DSL script for expressing the business rules. The proposed solution has been tested in two case studies. It is shown that the generator can help the implementation of the business rules in source codes and that the generated code can be used in business applications.