The invention provides an automatic rebounding device for a movable block, and the automatic rebounding device is used for movably arranging the movable block onto a body of a mould. The automatic rebounding device comprises a positioning block, a first locking nut, a second locking nut, a guide post, a positioning slot, a spring and a movable block, wherein when a core shooting mould is closed, the positioning block is pressed to move along the positioning slot, so that the movable block is driven to reach a predetermined position on the body of the mould; the spring is pressed, so that one end of the spring abuts against the positioning slot; and when the core shooting mould is opened, pressure borne on the tail end of the movable block is removed, so that the spring automatically rebounds to drive the positioning block to drive the movable block to return. The automatic rebounding device has the advantages of being simple in structure, convenient to operate, strong in applicability and the like, reduces dependency on labor power, improves manufacturing precision of a sand core, and effectively improves production efficiency.