1. A recommended keyword suggestion system comprising a database storage device, the system comprising: a keyword extracting unit to extract at least one keyword associated with a certain keyword from a related search word database stored in the database storage device; a display score providing unit to provide at least one display score for the at least one extracted keyword, each of the at least one display score being associated with an expected revenue from advertisement of each of the at least one extracted keyword; and a recommended keyword determining unit to determine at least one recommended keyword to be displayed for the certain keyword among the at least one extracted keyword, based on the provided at least one display score.