PURPOSE: To provide the titled extruder capable of extruding different kinds of materials continuously in the shape of uniform concentric cylinder, by forming a ring-shaped gap to extrude the sheath material wrapping the core material, and rotating the core-extruding nozzle and the outer nozzle to the same directions at different rate of revolution.

CONSTITUTION: The sheath material 2 is supplied from the kneader 1, delivered from the inner part of the cylinder 5 to its bottom, and passed through the gap 13 formed by the stationary ring 10, the outer nozzle 9 and the nozzle part 12. The sheath material 2 is sent downward in a uniform state by the combined actions of the nozzle part 12 furnished with small blades 7 at the outer surface and of the nozzle 9 rotating to the same direction to but at a different speed from the rotation of the nozzle part 12. The nozzle 9 plays the role of holding the core material 3 in the hollow part of the sheath material 2, and forms an accurate concentric cylinder having double-layer structure together with the core material 3 introduced at a constant rate. The extruder is used for the preparation of a cake containing bean jam, etc. as the core material.