To hold a cut piece by diameter-expanding a support arm by inserting the cut piece into a lower hole without installing an operation member such as a cylinder, to simplify a structure and reduce the structure in size, and to avoid the cut piece from falling down into a tank by holding the cut piece by using the support arm which is diameter-expanded when a hole formed by a rotating cutting blade is formed.
An engagement claw (47) engaged with a recess (23c) to be engaged in which a tip is formed at a shaft with respect to a slide board (41) movably arranged at a holder (25) in the axial direction is arranged so as to move in a state that the claw is energized to the axial orthogonal direction by an elastic force of a compression spring (49), the engagement claw (47) engaged with the recess (23c) to be engaged is moved to the engagement release direction by using an engagement release cam (43) which is arranged at the holder (25), and the holder (25) is made to be axially movable with respect to the shaft (23).