To provide an economical roll paper core tube having a structure in which a magnet portion in the core tube to be used for a drug subdividing apparatus can easily be replaced, making it easily applicable to various alterations of specification, and making a magnet not wasteful.

This roll paper core tube 11 is used for a drug subdividing apparatus having an angle sensor 14 for magnetically detecting a rotational angle with respect to a roll support cylinder 12 and a control unit 4 for controlling the supply of a sheet on the basis of the rotational angle of the roll support cylinder 12, which is detected by the angle sensor. This roll paper core tube 11 has a hollow core tube 19 around which a sheet of the roll paper is wound, a thin-walled cylindrical body 15 disposed in an insertable manner between an inner face of the hollow core tube and a support cylinder, and at least one magnet M disposed in the cylindrical body 15.