An axle assembly includes a first holding member, and a second holding member with a collet shape on a tubular body. The second holding member is inserted into a penetrating hole of a shaft mounting portion so as to reduce its diameter. The tubular body is directly inserted into the penetrating hole. When moving the fastening bar by operation of the cam lever, both holding members nip and hold the shaft mounting portion. While dismantling, a diameter shrinking part moves so as to reduce a diameter of the second holding member.