A chuck-claw guide structure includes a guide-space delimiting part that delimits a guide space in communication with an attachment groove, and a regulation part provided on the guide-space delimiting part. The guide-space delimiting part has a contact surface configured to regulate the claw in contact therewith at a position along the attachment groove in a first direction. The regulation part is configured to regulate the claw at a position along the attachment groove in a second direction different from the first direction.