PURPOSE: To provide a device for molding an intermediate product of a weatherstrip in which the protruding length of a lip section is gradually varied along the longitudinal direction without damaging the dimension accuracy after extrusion molding.

CONSTITUTION: An extrusion opening section 12 of cross sectional shape corresponding to the cross sectional shape of a lip section 3' is formed in a movable molding die 11 for forming a notch channel 41 on the lip section 3' of an intermediate product S'1 of a weatherstrip by varying the molding position. A notch channel forming blade 13 is disposed on one of inner faces facing each other of the extrusion opening section 12 by the arrangement, and the movable molding die 11 is mounted slidably on a front end face 8a of a basic molding die 8 in a manner that the movable molding die 11 is moved along the protruding direction of the lip section 3' of an intermediate product S'1 of the weatherstrip extrusion molded continuously from the basic mold die 8.