AbstractIn a description of the function of the central nervous system in forearm movement control, the structure of the central nervous system must be considered, together with the control function produced by that structure. In this paper, the motor signal is assumed to originate from the brain, and the forearm movement is defined as the combined cooperative processes (integration) of the reflexes in various portions of the central nervous system, including the brain reflex. Based on this concept, the macroscopic mechanism of the central nervous system is described insofar as this is possible. The forearm movement induced by visual stimulation is then considered, and the response is measured in the frequency domain. A model is constructed for the central functions that describes the frequency response over a relatively wide range and agrees well with the macroscopic mechanism of the central nervous system. This model can be regarded as representing the control‐information processing mechanism and function of the biological system in response to the external environment, reflecting the functions of the higher‐level portion of the central nervous system, i.e., the brain. With the proposed model the behavior can also correspond to the functions and mechanism of the lower levels, i.e., the brainstem‐spinal system, which seems to imply that the brain and brainstem‐spinal systems are similar in functional structure but process different info