A cushion assembly includes a retarding member, a support member and an urging member. The retarding member has a base portion and an upper portion formed with an upper end face, and is formed with a guiding hole extending inwardly and axially from the upper end face. The support member includes a support disc disposed above the upper end face of the retarding member, and a guiding post extending from the support disc into the guiding hole in the retarding member 4. The urging member is sleeved around the retarding member for urging the support disc upwardly and axially away from the retarding member.