A machine tool comprising: a tool post provided with a tool (T1) for machining a workpiece (W1); a rotating unit (U1) including a spindle provided with a chucking unit for releasably chucking the workpiece (W1) which is subjectable to machining by the tool (T1) mounted on the tool post ; a supporting unit (U2) which rotatably supports the spindle around an axis (AX1) of the spindle ; and a fluid supplying unit (U3) removably mounted on the supporting unit (U2) to supply fluid to the chucking unit via the spindle ; wherein, the fluid supplying unit (U3) has an insert (P1) to be received in the rotating unit (U1) in the direction of the axis of the spindle , and wherein the rotating unit (U1) has an inner circumferential surface (U1i) opposite an outer circumferential surface (P1o) of the insert (P1) received in the rotating unit (V1); wherein a labyrinth clearance (C1) is formed between the outer circumferential surface (P1o) of the insert (P1) and the inner circumferential surface (U1i) of the rotating unit (U1) in a state that the fluid supplying unit (U3) is mounted on the supporting unit (U2), the labyrinth clearance (C1) allowing rotation of the rotating unit (U1) and restricting leakage of the supplied fluid from inside the spindle when the rotating unit (U1) is rotated, and at a time that the fluid supplying unit (U3) is mounted on the supporting unit (U2) from a state that the fluid supplying unit (U3) is separated from the supporting unit (U2), the labyrinth clearance (C1) is formed by bringing a stop member provided on the outer circumference of the fluid supplying unit (U3) into contacting the supporting unit (U2). a tool post provided with a tool (T1) for machining a workpiece (W1); a rotating unit (U1) including a spindle provided with a chucking unit for releasably chucking the workpiece (W1) which is subjectable to machining by the tool (T1) mounted on the tool post ; a supporting unit (U2) which rotatably supports the spindle around an axis (AX1) of the spindle ; and a fluid supplying unit (U3) removably mounted on the supporting unit (U2) to supply fluid to the chucking unit via the spindle ; wherein, the fluid supplying unit (U3) has an insert (P1) to be received in the rotating unit (U1) in the direction of the axis of the spindle , and wherein the rotating unit (U1) has an inner circumferential surface (U1i) opposite an outer circumferential surface (P1o) of the insert (P1) received in the rotating unit (V1); wherein a labyrinth clearance (C1) is formed between the outer circumferential surface (P1o) of the insert (P1) and the inner circumferential surface (U1i) of the rotating unit (U1) in a state that the fluid supplying unit (U3) is mounted on the supporting unit (U2), the labyrinth clearance (C1) allowing rotation of the rotating unit (U1) and restricting leakage of the supplied fluid from inside the spindle when the rotating unit (U1) is rotated, and at a time that the fluid supplying unit (U3) is mounted on the supporting unit (U2) from a state that the fluid supplying unit (U3) is separated from the supporting unit (U2), the labyrinth clearance (C1) is formed by bringing a stop member provided on the outer circumference of the fluid supplying unit (U3) into contacting the supporting unit (U2). <EOS>