A design apparatus, a design method, and a program, which enable the design of a small-scale circuit that is high in serviceability and quality are provided. Plural commands described at a behavior level are separated into control system behaviors that are behaviors concerning control and data system behaviors that are behaviors concerning data transfer, the data system behaviors for the commands are integrated into one or more behaviors, and both the control system behaviors for the commands and the behavior obtained by integrating the data system behaviors for the commands are subjected to high-level synthesis.