We are investigating the effective facilitation methodology for the introduction of formal methods into actual software developments. One of the important issues is how to define and develop an adequate development process with formal methods. In this paper, we discuss this issue from a view point of software process improvement using a standard development process model, CMMI-DEV, which is a compilation of best practices in software development. We expect using the standard process model as a reference can facilitate common understanding for the advantages of formal methods and the comparison between actual instances of software process with formal methods. This approach leads to the exploitation of knowledge and findings obtained in the successful cases. We generate supportive hypotheses in the effect of formal methods on software development processes by using the standard improvement model. Then, we weakly examine them with a combination of a small-scale process, which has a strong relation to the organization level process, and a model-oriented formal method, VDM.