This paper presents C-based behavioral hardware design environment. Initially, we discuss motivations of the design environment and the merits and demerits of the C language as a behavioral hardware language. The configuration of the environment of which main component is a behavioral synthesizer \"Cyber", is presented. Then, we explain various aspects of the C-based design method using some design experiences for both control dominated circuits and data intensive circuits. Lastly, we summarize current status of our C-based design and discuss problems to diffuse C-based design method widely.