An object of the present invention is to obtain information corresponding to information, which is readable by sight, but no longer visible. The present invention provides a chuck mechanism comprising: a chuck body including an installation surface and a side surface; and a master jaw provided on the installation surface of the chuck body and configured to move in a radial direction of the chuck body, wherein a first marking is provided on the installation surface of the chuck body, the first marking is product information of the chuck mechanism, the product information has a readable form by sight, and at least one second marking is provided on the installation surface or the side surface of the chuck body, the second marking is information including at least the product information of the first marking, and the information of the second marking has a coded form.

A machine tool includes: a hollow spindle including a hollow portion along an axial direction; a plurality of chuck claws openably mounted at a distal end portion of the hollow spindle, and configured to hold a workpiece; an operation rod inserted into the hollow portion of the hollow spindle in a movable manner, and configured to close the plurality of chuck claws with movement of the operation rod toward one side in the axial direction and open the plurality of chuck claws with movement of the operation rod toward the other side in the axial direction; and a measuring apparatus configured to measure an opening dimension of the plurality of chuck claws based on a movement amount of the operation rod.

A workpiece holding device includes: a chuck including a chuck body, and a plurality of chuck claws openably supported on the chuck body and configured to hold a workpiece; an operation rod configured to drive the plurality of chuck claws for opening and closing with movement of the operation rod; and a measuring apparatus configured to measure an opening dimension of the plurality of chuck claws based on a movement amount of the operation rod.

An object of the present invention is to obtain information corresponding to information, which is readable by sight, but no longer visible. The present invention provides a chuck mechanism comprising: a chuck body including an installation surface and a side surface; and a master jaw provided on the installation surface of the chuck body and configured to move in a radial direction of the chuck body, wherein a first marking is provided on the installation surface of the chuck body, the first marking is product information of the chuck mechanism, the product information has a readable form by sight, and at least one second marking is provided on the installation surface or the side surface of the chuck body, the second marking is information including at least the product information of the first marking, and the information of the second marking has a coded form.

A machine tool includes: a hollow spindle including a hollow portion along an axial direction; a plurality of chuck claws openably mounted at a distal end portion of the hollow spindle, and configured to hold a workpiece; an operation rod inserted into the hollow portion of the hollow spindle in a movable manner, and configured to close the plurality of chuck claws with movement of the operation rod toward one side in the axial direction and open the plurality of chuck claws with movement of the operation rod toward the other side in the axial direction; and a measuring apparatus configured to measure an opening dimension of the plurality of chuck claws based on a movement amount of the operation rod.

A workpiece holding device includes: a chuck including a chuck body, and a plurality of chuck claws openably supported on the chuck body and configured to hold a workpiece; an operation rod configured to drive the plurality of chuck claws for opening and closing with movement of the operation rod; and a measuring apparatus configured to measure an opening dimension of the plurality of chuck claws based on a movement amount of the operation rod.