A cap-closing apparatus comprising: a holding mechanism section configured to be capable of holding a cap which is attached to an opening of a specimen container that is formed to be capable of containing a specimen; a rotating mechanism section configured to rotate the holding mechanism section; a support frame for supporting the holding mechanism section and the rotating mechanism section; a moving mechanism section configured to move the support frame; a torque detector configured to detect a torque at a time of rotation; and a controller configured to control an amount of rotation of the rotating mechanism section, based on the torque detected by the torque detector, wherein the holding mechanism section comprises a holding shaft comprising an engaging section configured to be engageable with the cap, wherein a screw portion is provided on an opening edge of the specimen container, and wherein an inner peripheral surface of an insertion portion, which is formed on one end side in an axial direction of the cap, is provided with a screw portion configured to be engaged with the screw portion of the specimen container, characterized in that a holding hole, in which the holding shaft of the holding mechanism section is inserted, is formed on the other end side in the axial direction of the cap, and a recess-and-projection portion, which is engaged with the engaging section, is formed in an inside of the holding hole; the recess-and-projection portion comprises a longitudinal plate extending in a radial direction in the holding hole, and in that the engaging section comprises a slit provided at a distal end of the holding shaft and configured such that the longitudinal plate is insertable in the slit, and an insertion portion having a tapered shape and provided between a plurality of the slits. a holding mechanism section configured to be capable of holding a cap which is attached to an opening of a specimen container that is formed to be capable of containing a specimen; a rotating mechanism section configured to rotate the holding mechanism section; a support frame for supporting the holding mechanism section and the rotating mechanism section; a moving mechanism section configured to move the support frame; a torque detector configured to detect a torque at a time of rotation; and a controller configured to control an amount of rotation of the rotating mechanism section, based on the torque detected by the torque detector, wherein the holding mechanism section comprises a holding shaft comprising an engaging section configured to be engageable with the cap, wherein a screw portion is provided on an opening edge of the specimen container, and wherein an inner peripheral surface of an insertion portion, which is formed on one end side in an axial direction of the cap, is provided with a screw portion configured to be engaged with the screw portion of the specimen container, a holding hole, in which the holding shaft of the holding mechanism section is inserted, is formed on the other end side in the axial direction of the cap, and a recess-and-projection portion, which is engaged with the engaging section, is formed in an inside of the holding hole; the recess-and-projection portion comprises a longitudinal plate extending in a radial direction in the holding hole, and in that the engaging section comprises a slit provided at a distal end of the holding shaft and configured such that the longitudinal plate is insertable in the slit, and an insertion portion having a tapered shape and provided between a plurality of the slits.