PURPOSE: To provide a continuous manufacture of a bar material which can make air-dried specific gravity low by making use of lightweight aggregate as a material and has moreover a smooth outer surface and thin open section.

CONSTITUTION: Mortar containing at least a binder and aggregate is cut down continuously and at a fixed thickness on a conveyor 12 for which a belt permeable to liquid is used, the cut down mortar is dehydrated gradually by a sucking mechanism 15 provided on the bottom part of the belt 11 permeable to liquid, the dehydrated mortar is put between the belt permeable to liquid and an upper belt and continuous pressure molding, is performed by passing the mortar through a gap having a thin open sectional form which is to be manufactured under this state.