This paper presents the development of an automatic test case generator (ATCG) for testing safety-critical software systems based on the concepts of specification-based testing. The ATCG receives the specification of system under test in normal specification language form and the causes and effects are automatically extracted and it also will visualize the cause-effect graph specification model. Finally test cases are generated by using cause-effect graph software testing methods in detail combined with Boolean operator techniques. Often in ATCGs too many test cases are created but the results are not always perfect. In testing our ATCG, experimental results showed that quality test cases are produced and that redundant test cases are ignored.