Renewable energies having little effect on the global environment have been attracting much attention. Among them, wind power has been introduced widely. However, output power of wind power generation is unstable, and thus it can have bad influence on power system operation. Therefore, control of the introduction or battery system for smoothing the unstable output is required. In this paper, a new method of power system frequency control is proposed which is based on the output frequency band control of wind farm by using variable speed wind generators.