Software testing is an important component in the software development life cycle, which leads to have the good quality of software product. Therefore, software industry needs to upgrade the testing process for high performance. The Testing Maturity Model (TMM) is one choice to apply for improving the testing process. It guides organization about framework of software testing. The TMM Assessment Model (TMM-AM) is a test process assessment model following the TMM. The TMM-AM consists of processes to assess test capability of organizations. Currently, the assessment process lacks of tools to be performed. This research proposes a supporting tool based on the TMM-AM which each organization can assess its testing process by itself. The tool can identify test maturity level for an organization and suggest procedures to reach its goal. The tool is developed to be use in four options depend on organizations that want to assess their testing process. The organizations use existing project’s test work products and the TMM questionnaire as input data for the assessment. We tested the tool with test case and four software development organizations. Three of the organizations have a good software development process referring to standard models such as the CMM, CMMI or TMM. The other one is an organization which has never applied any software process model to improve its software process. The result is that the TMM appraisal assistant tool can apply to be used in software organizations.