The calculations of NPV (net present value) and cash flows provide useful means when organizations come to decide whether they should transit from one-off development to software product line (SPL) based development, how much investment should be made for the development of SPL, whether their investments are being successfully returned from the on-going SPL adoption programs, or whether they should modify their on-going programs. The paper first summarizes experiences that were gathered from the Toshiba Software Factory in which a series of product lines for the domain of electric power generation, called EPG-SPL, has been developed and practically applied since 1962. At present, the 4th generation of EPG-SPL is being applied. The purpose of this paper is to present how NPV and cash flow calculations can be used if it is applied to the management and controls of SPL adoption, and to propose a guide for monitoring the shortage of return-oninvestment every year, which is necessary to achieve successful SPL adoptions.