| 摘要 |
PROBLEM TO BE SOLVED: To positively change a headstock into a turnable state and a state of being fixable onto a swivel base and to turn the headstock while supporting it in a stable state. SOLUTION: A rolling element holding member 58 is provided at the lower part of the headstock. The rolling element holding member 58 holds a rolling element 72 rotatably to the lower end part, and the rolling element 72 moves up and down between a receding position of receding upward from the lower face of the headstock, and a projecting position of projecting downward from the lower face of the headstock. When the rolling element holding member 58 is changed into the receding position, the headstock lands on a swivel base 42, and when the rolling element holding member 58 is changed into the projecting position, the headstock can travel turning on the swivel base 42 while being accompanied by rolling of the rolling element 72.
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