It remains important for a development organization to configure a software process that enables it to develop software products with the least possible number of defects after shipment. A development organization of CMMI level 5 has, over three years, been strived to improve those software projects that had been noted as having many defects after shipment. In this paper, we discuss our organization’s improvement (Kaizen) activities, to analyze the important matters of software process to be considered when developing a software product with the least possible number of defects after shipment. Our results are identified by three important points;1) early ensured quality by defect detection during design or code review;2) quality assurance for both process quality and product one;and 3) quantitative management by which data of the appropriate resolution can be collected at an appropriate timing.