In a molding die machining electrode, slit grooves of a molding die are machined with a slit groove forming part having a substantially circular outer circumference by ranging hexagonal erected wall parts in a row; while the inner circumference of a slit groove forming part overlaps with the erected wall parts in the outer circumference of the slit groove forming part, the outside slit grooves are machined with the slit groove forming part having a substantially circular outer circumference. The further outside slit grooves are machined with the slit groove forming part of the third electrode. A plurality of the slit groove forming parts are radially divided and overlapping portions between the plurality of the slit groove forming parts are formed substantially coaxially with a molded body. The areas of the slit groove forming parts are designed to nearly similar values, suppressing the difference in wear of the electrodes.