A retainer for a sliding device provided with a buffer member includes a body which is arranged between sliding rails, and has buffering insertion grooves on one side that are open in the outward direction, which is the withdrawal direction, and on the other side, which is the closing direction, so as to adjust the range of withdrawal when the sliding rails are withdrawn; and buffer member portions protruding from the two ends of the body, respectively, in the direction of an accommodation body, and being arranged so as to be respectively inserted into the buffering insertion grooves for coming into contact when the sliding rails are withdrawn.