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In the social context of an aging workforce in the labor intensive manufacturing sector, we discuss an assistance system for older workers (mainly in their 40's and 50's) who have excellent skills though their physical ability to perform iterative tasks at a constant speed with high quality over one eight hour shift has declined. "Skill-Assist" which is proposed in this paper is a new type of assisting system which varies its mechanical impedance to give workers who have been working under the lifetime employment system a sense of achievement in being again able to accomplish the skilled tasks they were capable of when younger. This paper discusses the control algorithm of Skill-Assist based on variable impedance control. First, a criterion for varying the impedance of Skill-Assist in response to task condition variations is explained. Second, impedance patterns experimentally determined to be desirable are discussed. These patterns are those required to produce a good subjective operational feel when maneuvering Skill-Assist and precise positioning based on the criterion for varying the impedance. Finally, the control algorithm of Skill-Assist is presented. This algorithm is estimated based on the subjective operational feel, physical stress, and productivity of one selected iterative positioning task.