The purpose of the present invention is to shift the conveyed bivalves onto a turn table promptly and smoothly, improve the drilling efficiency, and perform accurate drilling by improving accuracy in positioning the shifted bivalves. To achieve the purpose, a bivalve shifting device (38) for shifting bivalves, which are conveyed by a bivalve conveyance unit (20), onto a turn table (30), is installed at the turn table. The bivalve shifting device comprises rotary rollers (35), which are respectively installed at a plurality of tables (33) installed on the circumferential surface of a drum (32) of the turn table, which is intermittently rotated. The rotary rollers are rotated when the table is positioned at a shifting position (P1), and intermittently rotated so as to stop the rotation when the table is positioned at the drilling position (P2). The rotary rollers also function as a second position determining post (35) when the rotation of the rotary rollers is stopped. The rotary rollers obtain the rotary driving force when a slit plate (36), which is installed outside the drum to be able to rotate, is pressed at the shifting position.
