An improved bottle opening machine for smoothly removing crown caps from bottle necks of empty bottles contained in bottle cases which are being conveyed on a conveyance system in a single file, in which the cap removing is carried out by the steps of engaging of cap removing sections on rotary discs with the crown caps on the bottle necks in an area where the circular movement path of the cap removing sections and the linear movement path of the bottle necks mutually converge in the tangential direction, removing of the crown caps from the bottle necks under the influence of a moment which is produced as the former is separated from the latter as the rotary discs are rotated, and releasing of the removed crown caps from the cap removing sections with the aid of cap releasing mechanisms. To ensure that the cap removing sections are positioned correctly with corresponding bottle necks, at least a synchronizing means is rotatably mounted on the frame structure. The synchronizing means comprises a synchronizing disc disposed adjacent to the rotary discs fixedly mounted on the drum. Alternatively, the synchronizing means may comprise a star wheel adapted to be engaged to the barrel of the bottles. The rotary discs are preferably mounted on a pair of arms adapted to swing upward and downward about pivotal pins on the frame structure.