This thesis deals with man-on-board automated storage and retrieval systems which are widely used to store or retrieve the itmes of small quantities and light weight. Three kinds of order picking are analyzed in terms of expected travel times. Also, by varying the height of the horizontal limit line which divides the rack into two region, its effects on the travel times are determined. Finally the best policy among them is suggested and the good height of limit line for each policy to reduce the expected travel times are proposed.