To provide a core tube for an external heat type rotary furnace capable of preventing metallic contamination.

This core tube (2) for the external heat type rotary furnace is composed of a cylindrical body (20) heated from the external while rotated, and having engagement projecting sections (201-208) composed of non-metallic material such as ceramics and projecting from an inner peripheral face, and plate-shaped stirring plate (211-214) disposed in the cylindrical body, composed of non-metallic material such as ceramics, and revolving in the cylindrical body by being elevated by being engaged with the engagement projecting sections at ends. As the cylindrical body and the stirring plates are composed of the non-metallic material such as ceramics, mixing of metal into a heated object can be prevented, and further as the stirring plates revolve in a prescribed manner with the rotation of the cylindrical body, the heated object can be sufficiently stirred, scraped off and stripped off in the cylindrical body.