To reduce the outflow of crude rubber from a die and simply position an FRP core by using the first dies parting in the axial direction of a core section for molding the envelopes at both end sections of a polymer insulator constituted of a barrel section and flanges protruded from the barrel section and the second die parting in the radial direction of the flange for molding the envelope at the middle section of the polymer insulator.

This polymer insulator molding die 21 is constituted of the first dies made of ma pair of dies 23-1, 23-2 having parting surface at the flange tip outer peripheral position of a flange section 4-1 at the uppermost section and the flange tip outer peripheral position of a flange section 4-2 at the lowermost section at both ends and molding the portions of the P-face and Q-face of an envelope and the second die made of a pair of dies 22-1, 22-2 provided at the middle of the first dies and molding the portion other than the P-face and Q-face parting in the radial direction of the shade 4 of the polymer insulator 1. The first dies at both end seconds have no parting surface, crude rubber is saved at the time of compression molding, and positioning is simplified.