To separate a green sand and a core piece in a mold with a simple and unexpensive equipment by holding up and dropping recovering sand, disintegrating the green sand piece with the shock of dropping, screening into the sand and undisintegrating core piece, joining the sand into the recovered sand and feeding the core piece into a regenerating device.

The recovering sand is charged into a first rotary drum type screening device 2 through a belt conveyor 1. The recovering sand is dropped and disintegrated which rotating a screening body 4 in the first rotary drum type screening device 2 and also, the undisintegrating sand piece and the undisintegrating core piece in the green mold and the disintegrated sand are screened. The sand is temporarily stored into a storing mechanism 5. The undisintegrating sand piece and the undisintegrating core piece in the green mold are fed to a second rotary drum type screening device 3 through an introducing tube 18. The undisintegrating sand piece and core piece are applied with the same treatment in the second rotary drum type screening device 3 and the difficult-to-integrating core piece is fed to the core sand recovering device with a belt conveyor 20 through an introducing tube 19.