PURPOSE: To prevent the discharge of molding sand which is ununiform in a kneading condition by connecting a circulating chamber providing rotary blades on a kneading chamber having a supplying hole and a discharging hole which are freely opened/closed.

CONSTITUTION: At first, by starting a driving motor 7 and working a gate opening cylinder 3, a supplying gate 4 is opened and at the time of supplying raw material sand from a raw material sand tank 2, suitable quantities of a binder and hardening agent are added from a spraying nozzle 5. Thus, after gradually feeding forward the sand supplied from the supplying hole 6 to the kneading chamber 1 while scraping and kneading with plural rotary blades 10, the sand is discharged to the other part successively from the discharging hole 13 by working a gate opening cylinder 11 to open the discharging gate 12. Then, at the time of temporarily stopping and interruption by closing the supplying hole 6 and the discharging hole 13 in the kneading chamber 1, the sand remaining thereon is continued to circulate along a circulating passage 14 between the kneading chamber 1 and the circulating chamber 15 connected with the kneading chamber and the sand discharged just after reopening is sufficiently kneaded and can be used.